feat: dark/light theme toggle (Catppuccin Frappé ↔ Latte)

- app/config/theme.py: palette definitions for both themes + apply_qss()
  helper used by both main.py (startup) and MainWindow (live toggle)
- resources/style_light.qss: complete Catppuccin Latte QSS
- View menu: ☀️/🌙 Switch Theme action (Ctrl+Shift+T) toggles live
- Preferences → Appearance: Color theme dropdown persists choice
- SQLHighlighter: _build_rules() reads get_palette(); update_theme()
  rebuilds rules and rehighlights all open editors on switch
- SqlCompleter: popup stylesheet reads get_palette() via
  _apply_popup_style(); update_theme() called on switch
- EditableTableModel: dirty/delete cell colors read get_palette() live
- ResultTableModel: NULL_COLOR property reads get_palette() live
- TableViewer: apply_settings() refreshes frozen-view border + repaints

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -144,6 +144,7 @@ All four drivers have a `_where(where: dict) → (clause_str, params)` static he
 - Connection ping indicator: 30-second `_PingWorker` (QThread) pings each active connection via `test_connection()`; status dot (● green / ● red) shown in status bar right side with per-connection tooltip
 - Frozen first column in `TableViewer`: 📌 toggle button in toolbar; dual-view overlay (`_frozen_view` child of `_table_view`) with synced vertical scroll and row heights; event-filter updates geometry on resize
 - Keyboard navigation in dialogs: OK set as default button (Enter submits) in `RowDialog` and `ConnectionDialog`; focus jumps to first input field on open; Enter in password field submits `ConnectionDialog`
+- Light / dark theme toggle: `app/config/theme.py` holds Catppuccin Frappé (dark) + Latte (light) palettes; `resources/style_light.qss` is the full Latte QSS; toggle via View → Switch Theme (Ctrl+Shift+T) or Preferences → Color theme; on switch, QSS is reloaded, syntax highlighter rebuilds rules via `update_theme()`, completer popup recolors, and model dirty/NULL colors update live
 
 ### Not Yet Implemented
 **High impact:**
@@ -155,5 +156,4 @@ All four drivers have a `_where(where: dict) → (clause_str, params)` static he
 **Medium impact:**
 - Transaction panel: explicit BEGIN / COMMIT / ROLLBACK controls with in-flight indicator
 - Global schema search: search across all tables/columns/procedures in a database
-- Light theme: Catppuccin Latte or similar, toggle from Preferences
 - Schema diff: compare two database schemas and show structural differences

app/config/theme.py

@@ -0,0 +1,121 @@
+"""
+Theme palettes — Catppuccin Frappé (dark) and Catppuccin Latte (light).
+
+Usage:
+    from app.config.theme import get_palette, apply_qss, is_dark
+"""
+from pathlib import Path
+
+
+# ── Catppuccin Frappé ─────────────────────────────────────────────────────────
+DARK = {
+    "base":     "#303446",
+    "mantle":   "#292c3c",
+    "crust":    "#232634",
+    "surface0": "#414559",
+    "surface1": "#51576d",
+    "surface2": "#626880",
+    "overlay":  "#737994",
+    "subtext":  "#a5adce",
+    "text":     "#c6d0f5",
+    "blue":     "#8caaee",
+    "lavender": "#babbf1",
+    "green":    "#a6d189",
+    "teal":     "#81c8be",
+    "sky":      "#99d1db",
+    "red":      "#e78284",
+    "peach":    "#ef9f76",
+    "yellow":   "#e5c890",
+    "mauve":    "#ca9ee6",
+    # derived UI tokens
+    "gutter_bg":  "#2a2d3e",
+    "dirty_bg":   "#3a2f25",
+    "dirty_fg":   "#ef9f76",
+    "delete_bg":  "#3a2530",
+    "delete_fg":  "#e78284",
+    # syntax
+    "syn_keyword":  "#8caaee",
+    "syn_type":     "#ef9f76",
+    "syn_function": "#a6d189",
+    "syn_string":   "#a6d189",
+    "syn_number":   "#ef9f76",
+    "syn_comment":  "#737994",
+    "syn_operator": "#ca9ee6",
+    "syn_ident":    "#99d1db",
+    # completer popup
+    "popup_bg":       "#292c3c",
+    "popup_border":   "#51576d",
+    "popup_selected": "#414559",
+    "popup_hover":    "#363a4f",
+}
+
+# ── Catppuccin Latte ──────────────────────────────────────────────────────────
+LIGHT = {
+    "base":     "#eff1f5",
+    "mantle":   "#e6e9ef",
+    "crust":    "#dce0e8",
+    "surface0": "#ccd0da",
+    "surface1": "#bcc0cc",
+    "surface2": "#acb0be",
+    "overlay":  "#9ca0b0",
+    "subtext":  "#6c6f85",
+    "text":     "#4c4f69",
+    "blue":     "#1e66f5",
+    "lavender": "#7287fd",
+    "green":    "#40a02b",
+    "teal":     "#179299",
+    "sky":      "#04a5e5",
+    "red":      "#d20f39",
+    "peach":    "#fe640b",
+    "yellow":   "#df8e1d",
+    "mauve":    "#8839ef",
+    # derived UI tokens
+    "gutter_bg":  "#dce0e8",
+    "dirty_bg":   "#fff3e6",
+    "dirty_fg":   "#fe640b",
+    "delete_bg":  "#ffe8ed",
+    "delete_fg":  "#d20f39",
+    # syntax
+    "syn_keyword":  "#1e66f5",
+    "syn_type":     "#fe640b",
+    "syn_function": "#40a02b",
+    "syn_string":   "#40a02b",
+    "syn_number":   "#fe640b",
+    "syn_comment":  "#9ca0b0",
+    "syn_operator": "#8839ef",
+    "syn_ident":    "#04a5e5",
+    # completer popup
+    "popup_bg":       "#e6e9ef",
+    "popup_border":   "#bcc0cc",
+    "popup_selected": "#ccd0da",
+    "popup_hover":    "#d8dce8",
+}
+
+_QSS_DIR = Path(__file__).parent.parent.parent / "resources"
+
+
+def get_palette() -> dict:
+    """Return the color dict for the currently active theme."""
+    from app.config.settings import get_settings
+    name = get_settings().get("theme", "dark")
+    return DARK if name == "dark" else LIGHT
+
+
+def is_dark() -> bool:
+    from app.config.settings import get_settings
+    return get_settings().get("theme", "dark") == "dark"
+
+
+def qss_path(theme: str) -> Path:
+    name = "style" if theme == "dark" else "style_light"
+    return _QSS_DIR / f"{name}.qss"
+
+
+def apply_qss(app, theme: str = None) -> None:
+    """Load and apply the QSS for *theme* (defaults to current setting)."""
+    from app.config.settings import get_settings
+    if theme is None:
+        theme = get_settings().get("theme", "dark")
+    path = qss_path(theme)
+    if path.exists():
+        app.setStyleSheet(path.read_text(encoding="utf-8"))

app/main_window.py

@@ -17,6 +17,7 @@ from PyQt6.QtWidgets import (
 )
 from PyQt6.QtCore import Qt, QTimer, QThread, pyqtSignal
 from PyQt6.QtGui import QAction, QColor, QKeySequence
+from app.config.theme import apply_qss, is_dark
 
 from app.ui.schema_browser    import SchemaBrowser
 from app.ui.sql_editor        import SQLEditorWidget
@@ -208,6 +209,12 @@ class MainWindow(QMainWindow):
         view_menu.addAction(self._act("Toggle Query History", self._toggle_history, "Ctrl+Shift+H"))
         view_menu.addAction(self._act("New SQL Tab", self._new_sql_tab, "Ctrl+T"))
         view_menu.addAction(self._act("Close Tab", self._close_current_tab, "Ctrl+W"))
+        view_menu.addSeparator()
+        self._theme_action = QAction("", self)
+        self._theme_action.setShortcut(QKeySequence("Ctrl+Shift+T"))
+        self._theme_action.triggered.connect(self._toggle_theme)
+        self._update_theme_action_label()
+        view_menu.addAction(self._theme_action)
 
         # ── Tools ─────────────────────────────────────────────────────────────
         tools_menu = mb.addMenu("&Tools")
@@ -662,9 +669,29 @@ class MainWindow(QMainWindow):
 
     def _open_preferences(self):
         dlg = PreferencesDialog(parent=self)
-        dlg.settings_applied.connect(self._apply_settings_to_open_tabs)
+        dlg.settings_applied.connect(self._on_settings_applied)
         dlg.exec()
 
+    def _on_settings_applied(self):
+        apply_qss(QApplication.instance())
+        self._update_theme_action_label()
+        self._apply_settings_to_open_tabs()
+
+    def _toggle_theme(self):
+        from app.config.settings import get_settings
+        new_theme = "light" if is_dark() else "dark"
+        get_settings().set("theme", new_theme)
+        get_settings().save()
+        apply_qss(QApplication.instance(), new_theme)
+        self._update_theme_action_label()
+        self._apply_settings_to_open_tabs()
+
+    def _update_theme_action_label(self):
+        if is_dark():
+            self._theme_action.setText("☀️  Switch to Light Theme")
+        else:
+            self._theme_action.setText("🌙  Switch to Dark Theme")
+
     def _apply_settings_to_open_tabs(self):
         """Push updated settings to all currently open workspace tabs."""
         for i in range(self._workspace.count()):

app/models/result_table_model.py

@@ -7,11 +7,15 @@ from PyQt6.QtCore import (
 )
 from PyQt6.QtGui import QColor, QFont
 
+from app.config.theme import get_palette
+
 
 class ResultTableModel(QAbstractTableModel):
     """Immutable result-set model — replaces data via set_data()."""
 
-    NULL_COLOR  = QColor("#737994")   # muted grey for NULL
+    @property
+    def NULL_COLOR(self):
+        return QColor(get_palette()["overlay"])
     NUM_ALIGN   = Qt.AlignmentFlag.AlignRight | Qt.AlignmentFlag.AlignVCenter
     TEXT_ALIGN  = Qt.AlignmentFlag.AlignLeft  | Qt.AlignmentFlag.AlignVCenter
 

app/ui/preferences_dialog.py

@@ -10,6 +10,8 @@ from app.config.settings import get_settings
 _FONT_FAMILIES = ["Consolas", "JetBrains Mono", "Fira Code", "Cascadia Code", "Courier New"]
 _PAGE_SIZES    = [50, 100, 500, 1000, 0]   # 0 → All
 _PAGE_LABELS   = ["50", "100", "500", "1 000", "All"]
+_THEMES        = [("dark",  "🌙  Dark  (Catppuccin Frappé)"),
+                  ("light", "☀️  Light (Catppuccin Latte)")]
 
 
 class PreferencesDialog(QDialog):
@@ -64,6 +66,18 @@ class PreferencesDialog(QDialog):
 
         root.addWidget(results_box)
 
+        # ── Appearance ────────────────────────────────────────────────────────
+        appear_box = QGroupBox("Appearance")
+        af = QFormLayout(appear_box)
+        af.setSpacing(8)
+
+        self._theme = QComboBox()
+        for _, label in _THEMES:
+            self._theme.addItem(label)
+        af.addRow("Color theme:", self._theme)
+
+        root.addWidget(appear_box)
+
         # ── General ───────────────────────────────────────────────────────────
         general_box = QGroupBox("General")
         gf = QFormLayout(general_box)
@@ -82,7 +96,7 @@ class PreferencesDialog(QDialog):
         root.addStretch()
 
         # ── Buttons ───────────────────────────────────────────────────────────
-        note = QLabel("Font changes take effect immediately in open editors.")
+        note = QLabel("Theme and font changes take effect immediately.")
         note.setObjectName("statusLabel")
         root.addWidget(note)
 
@@ -116,6 +130,10 @@ class PreferencesDialog(QDialog):
         self._max_history.setValue(s.get("max_history", 500))
         self._auto_commit.setChecked(s.get("auto_commit", True))
 
+        theme_name = s.get("theme", "dark")
+        ti = next((i for i, (k, _) in enumerate(_THEMES) if k == theme_name), 0)
+        self._theme.setCurrentIndex(ti)
+
     def _apply(self):
         s = get_settings()
         s.set("font_family",      self._font_family.currentText())
@@ -125,6 +143,7 @@ class PreferencesDialog(QDialog):
         s.set("query_timeout",    self._timeout.value())
         s.set("max_history",      self._max_history.value())
         s.set("auto_commit",      self._auto_commit.isChecked())
+        s.set("theme",            _THEMES[self._theme.currentIndex()][0])
         s.save()
         self.settings_applied.emit()
 

app/ui/sql_completer.py

@@ -12,6 +12,7 @@ from PyQt6.QtWidgets import QApplication, QListWidget, QListWidgetItem
 
 from app.ui.syntax_highlighter import _KEYWORDS, _TYPES, _FUNCTIONS
 from app.utils.worker import SchemaWorker
+from app.config.theme import get_palette
 
 # Combined, deduplicated keyword list used as the static completion pool.
 SQL_KEYWORDS: list[str] = list(dict.fromkeys(_KEYWORDS + _TYPES + _FUNCTIONS))
@@ -51,24 +52,28 @@ class _CompletionPopup(QListWidget):
         self.setFont(font)
         self._row_h = QFontMetrics(font).height() + 6
 
-        self.setStyleSheet("""
+        self._apply_popup_style()
-            QListWidget {
+        self.setVerticalScrollBarPolicy(Qt.ScrollBarPolicy.ScrollBarAsNeeded)
-                background: #292c3c;
+        self.setHorizontalScrollBarPolicy(Qt.ScrollBarPolicy.ScrollBarAlwaysOff)
-                color: #c6d0f5;
+
-                border: 1px solid #51576d;
+    def _apply_popup_style(self):
+        p = get_palette()
+        self.setStyleSheet(f"""
+            QListWidget {{
+                background: {p['popup_bg']};
+                color: {p['text']};
+                border: 1px solid {p['popup_border']};
                 border-radius: 4px;
                 padding: 2px;
                 outline: none;
-            }
+            }}
-            QListWidget::item { padding: 2px 8px; }
+            QListWidget::item {{ padding: 2px 8px; }}
-            QListWidget::item:selected {
+            QListWidget::item:selected {{
-                background: #414559;
+                background: {p['popup_selected']};
-                color: #c6d0f5;
+                color: {p['text']};
-            }
+            }}
-            QListWidget::item:hover { background: #363a4f; }
+            QListWidget::item:hover {{ background: {p['popup_hover']}; }}
         """)
-        self.setVerticalScrollBarPolicy(Qt.ScrollBarPolicy.ScrollBarAsNeeded)
-        self.setHorizontalScrollBarPolicy(Qt.ScrollBarPolicy.ScrollBarAlwaysOff)
 
         self.itemClicked.connect(
             lambda item: self._editor._completer._accept_completion(item.text())
@@ -142,6 +147,10 @@ class SqlCompleter(QObject):
 
     # ── Public API ────────────────────────────────────────────────────────────
 
+    def update_theme(self) -> None:
+        """Reapply popup colors after a theme change."""
+        self._popup._apply_popup_style()
+
     def set_context(self, driver, database: str) -> None:
         """Update the active driver/database and refresh schema cache."""
         self._driver   = driver

app/ui/sql_editor.py

@@ -471,7 +471,7 @@ class EditorTab(QWidget):
         self._splitter.setHandleWidth(3)
 
         self._editor = CodeEditor()
-        SQLHighlighter(self._editor.document())
+        self._highlighter = SQLHighlighter(self._editor.document())
         self._completer = SqlCompleter(self._editor, parent=self)
         self._editor.set_completer(self._completer)
         if self._driver:
@@ -603,6 +603,8 @@ class EditorTab(QWidget):
 
     def apply_settings(self) -> None:
         self._editor.apply_settings()
+        self._highlighter.update_theme()
+        self._completer.update_theme()
 
 
 # ── Tabbed SQL editor container ───────────────────────────────────────────────

app/ui/syntax_highlighter.py

@@ -1,6 +1,7 @@
 """
 SQL syntax highlighter for QPlainTextEdit.
 Highlights keywords, types, functions, strings, comments, and numbers.
+Colors follow the active Catppuccin theme (dark = Frappé, light = Latte).
 """
 import re
 from PyQt6.QtCore import QRegularExpression, Qt
@@ -8,6 +9,8 @@ from PyQt6.QtGui import (
     QSyntaxHighlighter, QTextCharFormat, QColor, QFont
 )
 
+from app.config.theme import get_palette
+
 
 def _fmt(color: str, bold: bool = False, italic: bool = False) -> QTextCharFormat:
     f = QTextCharFormat()
@@ -17,17 +20,7 @@ def _fmt(color: str, bold: bool = False, italic: bool = False) -> QTextCharForma
     return f
 
 
-# ── Token categories (Catppuccin Frappé palette) ─────────────────────────────
+# ── Keyword lists (shared with completer) ─────────────────────────────────────
-_KEYWORD_FMT   = _fmt("#8caaee", bold=True)   # blue   — DDL/DML/control
-_TYPE_FMT      = _fmt("#ef9f76")               # peach  — data types
-_FUNCTION_FMT  = _fmt("#a6d189")               # green  — functions
-_STRING_FMT    = _fmt("#a6d189")               # green  — string literals
-_NUMBER_FMT    = _fmt("#ef9f76")               # orange — numeric literals
-_COMMENT_FMT   = _fmt("#737994", italic=True)  # grey   — comments
-_OPERATOR_FMT  = _fmt("#ca9ee6")               # mauve  — operators/special
-_STAR_FMT      = _fmt("#ca9ee6", bold=True)    # mauve  — * wildcard
-
-# ── Keyword lists ─────────────────────────────────────────────────────────────
 _KEYWORDS = [
     "SELECT", "FROM", "WHERE", "JOIN", "LEFT", "RIGHT", "INNER", "OUTER",
     "FULL", "CROSS", "ON", "AS", "AND", "OR", "NOT", "IN", "LIKE", "BETWEEN",
@@ -79,56 +72,56 @@ class SQLHighlighter(QSyntaxHighlighter):
     def __init__(self, document):
         super().__init__(document)
         self._rules: list[tuple] = []
+        self._build_rules()
+
+    def _build_rules(self):
+        p = get_palette()
 
         def kw_pattern(words: list[str]) -> str:
             return r"\b(?:" + "|".join(words) + r")\b"
 
+        ci = QRegularExpression.PatternOption.CaseInsensitiveOption
         self._rules = [
-            # Keywords (case-insensitive handled via flag)
+            (QRegularExpression(kw_pattern(_KEYWORDS), ci),
-            (QRegularExpression(kw_pattern(_KEYWORDS),
+             _fmt(p["syn_keyword"], bold=True)),
-                                QRegularExpression.PatternOption.CaseInsensitiveOption),
+            (QRegularExpression(kw_pattern(_TYPES), ci),
-             _KEYWORD_FMT),
+             _fmt(p["syn_type"])),
-            # Data types
+            (QRegularExpression(kw_pattern(_FUNCTIONS), ci),
-            (QRegularExpression(kw_pattern(_TYPES),
+             _fmt(p["syn_function"])),
-                                QRegularExpression.PatternOption.CaseInsensitiveOption),
+            (QRegularExpression(r"\b\d+(\.\d+)?\b"),
-             _TYPE_FMT),
+             _fmt(p["syn_number"])),
-            # Functions
+            (QRegularExpression(r"'[^'\\]*(?:\\.[^'\\]*)*'"),
-            (QRegularExpression(kw_pattern(_FUNCTIONS),
+             _fmt(p["syn_string"])),
-                                QRegularExpression.PatternOption.CaseInsensitiveOption),
+            (QRegularExpression(r'"[^"]*"'),
-             _FUNCTION_FMT),
+             _fmt(p["syn_ident"])),
-            # Numbers
+            (QRegularExpression(r"`[^`]*`"),
-            (QRegularExpression(r"\b\d+(\.\d+)?\b"), _NUMBER_FMT),
+             _fmt(p["syn_ident"])),
-            # Single-quoted strings
+            (QRegularExpression(
-            (QRegularExpression(r"'[^'\\]*(?:\\.[^'\\]*)*'"), _STRING_FMT),
+                r"\bSELECT\s+\*|\*(?=\s*FROM)", ci),
-            # Double-quoted identifiers
+             _fmt(p["syn_operator"], bold=True)),
-            (QRegularExpression(r'"[^"]*"'), _fmt("#99d1db")),
+            (QRegularExpression(r"[=<>!%&|^~+\-*/]"),
-            # Backtick identifiers (MySQL)
+             _fmt(p["syn_operator"])),
-            (QRegularExpression(r"`[^`]*`"), _fmt("#99d1db")),
+            (QRegularExpression(r"--[^\n]*"),
-            # * wildcard
+             _fmt(p["syn_comment"], italic=True)),
-            (QRegularExpression(r"\bSELECT\s+\*|\*(?=\s*FROM)",
+            (QRegularExpression(r"#[^\n]*"),
-                                QRegularExpression.PatternOption.CaseInsensitiveOption),
+             _fmt(p["syn_comment"], italic=True)),
-             _STAR_FMT),
-            # Operators
-            (QRegularExpression(r"[=<>!%&|^~+\-*/]"), _OPERATOR_FMT),
-            # Single-line comment  --
-            (QRegularExpression(r"--[^\n]*"), _COMMENT_FMT),
-            # Single-line comment  #
-            (QRegularExpression(r"#[^\n]*"), _COMMENT_FMT),
         ]
-
+        self._comment_fmt = _fmt(p["syn_comment"], italic=True)
-        # Multi-line block comment  /* ... */
         self._block_comment_start = QRegularExpression(r"/\*")
         self._block_comment_end   = QRegularExpression(r"\*/")
 
+    def update_theme(self):
+        """Rebuild color rules for the current theme and re-highlight."""
+        self._build_rules()
+        self.rehighlight()
+
     def highlightBlock(self, text: str) -> None:
-        # Single-line rules
         for pattern, fmt in self._rules:
             it = pattern.globalMatch(text)
             while it.hasNext():
                 m = it.next()
                 self.setFormat(m.capturedStart(), m.capturedLength(), fmt)
 
-        # Multi-line block comments
         self.setCurrentBlockState(0)
         start_idx = 0
         if self.previousBlockState() != 1:
@@ -139,10 +132,10 @@ class SQLHighlighter(QSyntaxHighlighter):
             end_m = self._block_comment_end.match(text, start_idx)
             if end_m.hasMatch():
                 end_idx = end_m.capturedStart() + end_m.capturedLength()
-                self.setFormat(start_idx, end_idx - start_idx, _COMMENT_FMT)
+                self.setFormat(start_idx, end_idx - start_idx, self._comment_fmt)
                 m = self._block_comment_start.match(text, end_idx)
                 start_idx = m.capturedStart() if m.hasMatch() else -1
             else:
                 self.setCurrentBlockState(1)
-                self.setFormat(start_idx, len(text) - start_idx, _COMMENT_FMT)
+                self.setFormat(start_idx, len(text) - start_idx, self._comment_fmt)
                 break

app/ui/table_viewer.py

@@ -22,6 +22,7 @@ from PyQt6.QtGui import QColor, QBrush, QFont, QKeySequence, QShortcut
 
 from app.utils.worker import TableDataWorker
 from app.config.settings import get_settings
+from app.config.theme import get_palette
 
 
 # ─────────────────────────────────────────────────────────────────────────────
@@ -148,18 +149,20 @@ class EditableTableModel(QAbstractTableModel):
             return "" if val is None else str(val)
 
         if role == Qt.ItemDataRole.ForegroundRole:
+            p = get_palette()
             if self._is_deleted_row(r):
-                return QBrush(QColor("#e78284"))   # red — pending delete
+                return QBrush(QColor(p["delete_fg"]))
             if (r, c) in self._dirty:
-                return QBrush(QColor("#ef9f76"))   # orange — edited
+                return QBrush(QColor(p["dirty_fg"]))
             if val is None:
-                return QBrush(QColor("#737994"))   # grey — NULL
+                return QBrush(QColor(p["overlay"]))
 
         if role == Qt.ItemDataRole.BackgroundRole:
+            p = get_palette()
             if self._is_deleted_row(r):
-                return QBrush(QColor("#3a2530"))
+                return QBrush(QColor(p["delete_bg"]))
             if (r, c) in self._dirty:
-                return QBrush(QColor("#3a2f25"))
+                return QBrush(QColor(p["dirty_bg"]))
 
         return None
 
@@ -444,7 +447,7 @@ class TableViewer(QWidget):
         self._frozen_view.horizontalHeader().setSectionResizeMode(
             QHeaderView.ResizeMode.Fixed)
         self._frozen_view.setStyleSheet(
-            "QTableView { border: none; border-right: 2px solid #8caaee; }")
+            f"QTableView {{ border: none; border-right: 2px solid {get_palette()['blue']}; }}")
         self._frozen_view.hide()
 
         # Sync vertical scroll between the two views
@@ -887,6 +890,12 @@ class TableViewer(QWidget):
             )
         QApplication.clipboard().setText("\n".join(statements))
 
+    def apply_settings(self):
+        """Called by MainWindow when preferences (including theme) change."""
+        self._frozen_view.setStyleSheet(
+            f"QTableView {{ border: none; border-right: 2px solid {get_palette()['blue']}; }}")
+        self._model.layoutChanged.emit()   # repaint dirty/delete cells
+
     def _filter_by_cell(self, index):
         if not index.isValid():
             return

main.py

@@ -9,15 +9,13 @@ from PyQt6.QtGui import QFont
 
 from app.utils.logger import setup_logging, install_qt_message_handler, get_logger
 from app.main_window import MainWindow
+from app.config.theme import apply_qss
 
 log = get_logger(__name__)
 
 
 def load_stylesheet(app: QApplication) -> None:
-    style_path = os.path.join(os.path.dirname(__file__), "resources", "style.qss")
+    apply_qss(app)   # reads theme from settings, falls back to dark
-    if os.path.exists(style_path):
-        with open(style_path, "r", encoding="utf-8") as f:
-            app.setStyleSheet(f.read())
 
 
 def main():

resources/style_light.qss

@@ -0,0 +1,599 @@
+/* ═══════════════════════════════════════════════════════════════════════════
+   DBClient — Light Theme (Catppuccin Latte palette)
+   ═══════════════════════════════════════════════════════════════════════════ */
+
+/* ── Variables via flat tokens ─────────────────────────────────────────────
+   base      #eff1f5   crust     #dce0e8
+   surface0  #ccd0da   surface1  #bcc0cc   surface2  #acb0be
+   overlay   #9ca0b0   subtext   #6c6f85   text      #4c4f69
+   blue      #1e66f5   lavender  #7287fd   sapphire  #209fb5
+   green     #40a02b   teal      #179299   sky       #04a5e5
+   mauve     #8839ef   pink      #ea76cb   red       #d20f39
+   peach     #fe640b   yellow    #df8e1d
+   ─────────────────────────────────────────────────────────────────────── */
+
+/* ── Global reset ───────────────────────────────────────────────────────── */
+* {
+    outline: none;
+}
+
+QMainWindow, QDialog {
+    background-color: #eff1f5;
+    color: #4c4f69;
+}
+
+QWidget {
+    background-color: #eff1f5;
+    color: #4c4f69;
+    font-family: "Segoe UI", "Inter", sans-serif;
+    font-size: 10pt;
+}
+
+/* ── Menu bar ───────────────────────────────────────────────────────────── */
+QMenuBar {
+    background-color: #dce0e8;
+    color: #4c4f69;
+    border-bottom: 1px solid #ccd0da;
+    padding: 2px 0;
+}
+
+QMenuBar::item {
+    padding: 4px 12px;
+    border-radius: 4px;
+}
+
+QMenuBar::item:selected {
+    background-color: #ccd0da;
+}
+
+QMenu {
+    background-color: #e6e9ef;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    padding: 4px;
+}
+
+QMenu::item {
+    padding: 6px 24px 6px 12px;
+    border-radius: 4px;
+    color: #4c4f69;
+}
+
+QMenu::item:selected {
+    background-color: #ccd0da;
+    color: #4c4f69;
+}
+
+QMenu::separator {
+    height: 1px;
+    background: #bcc0cc;
+    margin: 4px 8px;
+}
+
+/* ── Status bar ─────────────────────────────────────────────────────────── */
+QStatusBar {
+    background-color: #dce0e8;
+    border-top: 1px solid #ccd0da;
+    color: #6c6f85;
+    font-size: 9pt;
+    padding: 2px 8px;
+}
+
+/* ── Scrollbars ─────────────────────────────────────────────────────────── */
+QScrollBar:vertical {
+    background: #eff1f5;
+    width: 10px;
+    margin: 0;
+}
+
+QScrollBar::handle:vertical {
+    background: #bcc0cc;
+    border-radius: 5px;
+    min-height: 24px;
+}
+
+QScrollBar::handle:vertical:hover {
+    background: #acb0be;
+}
+
+QScrollBar:horizontal {
+    background: #eff1f5;
+    height: 10px;
+}
+
+QScrollBar::handle:horizontal {
+    background: #bcc0cc;
+    border-radius: 5px;
+    min-width: 24px;
+}
+
+QScrollBar::handle:horizontal:hover {
+    background: #acb0be;
+}
+
+QScrollBar::add-line, QScrollBar::sub-line { height: 0; width: 0; }
+QScrollBar::add-page, QScrollBar::sub-page { background: transparent; }
+
+/* ── Splitter ────────────────────────────────────────────────────────────── */
+QSplitter::handle {
+    background-color: #ccd0da;
+}
+
+QSplitter::handle:horizontal { width: 2px; }
+QSplitter::handle:vertical   { height: 2px; }
+
+QSplitter::handle:hover {
+    background-color: #1e66f5;
+}
+
+/* ── Sidebar ─────────────────────────────────────────────────────────────── */
+#sidebarHeader {
+    background-color: #e6e9ef;
+    border-bottom: 1px solid #ccd0da;
+}
+
+#sidebarTitle {
+    color: #1e66f5;
+    font-size: 11pt;
+    font-weight: 600;
+}
+
+#newConnBtn {
+    background-color: #ccd0da;
+    color: #1e66f5;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    font-size: 14pt;
+    padding: 0;
+}
+
+#newConnBtn:hover {
+    background-color: #bcc0cc;
+    color: #7287fd;
+}
+
+/* ── Tree widget ─────────────────────────────────────────────────────────── */
+QTreeWidget {
+    background-color: #e6e9ef;
+    border: none;
+    color: #4c4f69;
+    font-size: 10pt;
+    show-decoration-selected: 1;
+}
+
+QTreeWidget::item {
+    padding: 3px 4px;
+    border-radius: 4px;
+}
+
+QTreeWidget::item:hover {
+    background-color: #d8dce8;
+}
+
+QTreeWidget::item:selected {
+    background-color: #ccd0da;
+    color: #4c4f69;
+}
+
+QTreeWidget::branch {
+    background: transparent;
+}
+
+/* ── Tab widget ──────────────────────────────────────────────────────────── */
+QTabWidget::pane {
+    border: none;
+    border-top: 1px solid #ccd0da;
+    background-color: #eff1f5;
+}
+
+QTabBar {
+    background-color: #e6e9ef;
+}
+
+QTabBar::tab {
+    background-color: #e6e9ef;
+    color: #6c6f85;
+    padding: 7px 16px;
+    border: none;
+    border-right: 1px solid #ccd0da;
+    font-size: 10pt;
+}
+
+QTabBar::tab:selected {
+    background-color: #eff1f5;
+    color: #4c4f69;
+    border-bottom: 2px solid #1e66f5;
+}
+
+QTabBar::tab:hover:!selected {
+    background-color: #d0d4e0;
+    color: #4c4f69;
+}
+
+QTabBar::close-button {
+    subcontrol-position: right;
+    padding: 2px;
+}
+
+/* ── Table view ──────────────────────────────────────────────────────────── */
+QTableView, QTableWidget {
+    background-color: #eff1f5;
+    alternate-background-color: #e6e9ef;
+    gridline-color: #ccd0da;
+    color: #4c4f69;
+    border: none;
+    selection-background-color: #ccd0da;
+    selection-color: #4c4f69;
+    font-size: 10pt;
+}
+
+QTableView::item, QTableWidget::item {
+    padding: 2px 6px;
+}
+
+QHeaderView {
+    background-color: #e6e9ef;
+}
+
+QHeaderView::section {
+    background-color: #e6e9ef;
+    color: #1e66f5;
+    border: none;
+    border-right: 1px solid #ccd0da;
+    border-bottom: 1px solid #ccd0da;
+    padding: 4px 8px;
+    font-weight: 600;
+}
+
+QHeaderView::section:hover {
+    background-color: #d0d4e0;
+}
+
+/* ── Plain text edit (SQL editor body) ───────────────────────────────────── */
+QPlainTextEdit {
+    background-color: #eff1f5;
+    color: #4c4f69;
+    border: none;
+    selection-background-color: #bcc0cc;
+    font-family: "Consolas", "JetBrains Mono", "Courier New", monospace;
+    font-size: 13pt;
+    line-height: 1.5;
+}
+
+/* ── Line number gutter ──────────────────────────────────────────────────── */
+LineNumberArea {
+    background-color: #dce0e8;
+}
+
+/* ── Buttons ─────────────────────────────────────────────────────────────── */
+QPushButton {
+    background-color: #ccd0da;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    padding: 5px 14px;
+    font-size: 10pt;
+}
+
+QPushButton:hover {
+    background-color: #bcc0cc;
+    border-color: #acb0be;
+}
+
+QPushButton:pressed {
+    background-color: #d0d4de;
+}
+
+QPushButton:disabled {
+    color: #acb0be;
+    background-color: #d0d4de;
+    border-color: #ccd0da;
+}
+
+#runBtn {
+    background-color: #40a02b;
+    color: #eff1f5;
+    font-weight: 700;
+    border: none;
+}
+
+#runBtn:hover {
+    background-color: #179299;
+}
+
+#stopBtn {
+    background-color: #d20f39;
+    color: #eff1f5;
+    font-weight: 700;
+    border: none;
+}
+
+#stopBtn:hover {
+    background-color: #e5394b;
+}
+
+#commitBtn {
+    background-color: #40a02b;
+    color: #eff1f5;
+    font-weight: 700;
+    border: none;
+}
+
+#rollbackBtn {
+    background-color: #fe640b;
+    color: #eff1f5;
+    font-weight: 700;
+    border: none;
+}
+
+#crudAddBtn {
+    background-color: #ccd0da;
+    color: #40a02b;
+    border: 1px solid #40a02b;
+    font-weight: 600;
+}
+
+#crudAddBtn:hover {
+    background-color: #40a02b;
+    color: #eff1f5;
+}
+
+#crudDeleteBtn {
+    background-color: #ccd0da;
+    color: #d20f39;
+    border: 1px solid #d20f39;
+    font-weight: 600;
+}
+
+#crudDeleteBtn:hover {
+    background-color: #d20f39;
+    color: #eff1f5;
+}
+
+/* ── Line edit ───────────────────────────────────────────────────────────── */
+QLineEdit {
+    background-color: #e6e9ef;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    padding: 5px 10px;
+    font-size: 10pt;
+    selection-background-color: #1e66f5;
+    selection-color: #eff1f5;
+}
+
+QLineEdit:focus {
+    border-color: #1e66f5;
+}
+
+QLineEdit::placeholder {
+    color: #acb0be;
+}
+
+/* ── Combo box ───────────────────────────────────────────────────────────── */
+QComboBox {
+    background-color: #e6e9ef;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    padding: 5px 10px;
+    font-size: 10pt;
+}
+
+QComboBox:focus {
+    border-color: #1e66f5;
+}
+
+QComboBox::drop-down {
+    border: none;
+    width: 24px;
+}
+
+QComboBox QAbstractItemView {
+    background-color: #e6e9ef;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    selection-background-color: #ccd0da;
+}
+
+/* ── Spin box ────────────────────────────────────────────────────────────── */
+QSpinBox {
+    background-color: #e6e9ef;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    padding: 4px 8px;
+}
+
+QSpinBox:focus { border-color: #1e66f5; }
+
+QSpinBox::up-button, QSpinBox::down-button {
+    background-color: #bcc0cc;
+    border: none;
+    border-radius: 3px;
+    width: 16px;
+}
+
+/* ── Check box ───────────────────────────────────────────────────────────── */
+QCheckBox {
+    color: #4c4f69;
+    spacing: 8px;
+}
+
+QCheckBox::indicator {
+    width: 16px;
+    height: 16px;
+    border: 2px solid #bcc0cc;
+    border-radius: 4px;
+    background: #e6e9ef;
+}
+
+QCheckBox::indicator:checked {
+    background-color: #1e66f5;
+    border-color: #1e66f5;
+}
+
+/* ── Dialog ──────────────────────────────────────────────────────────────── */
+QDialog {
+    background-color: #eff1f5;
+}
+
+QDialogButtonBox QPushButton {
+    min-width: 80px;
+}
+
+/* ── Form layout labels ──────────────────────────────────────────────────── */
+QFormLayout QLabel {
+    color: #6c6f85;
+}
+
+/* ── Tab widget in dialogs ───────────────────────────────────────────────── */
+QTabWidget#dialogTabs::pane {
+    border: 1px solid #ccd0da;
+    border-radius: 6px;
+    margin-top: -1px;
+}
+
+/* ── Group box ───────────────────────────────────────────────────────────── */
+QGroupBox {
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    margin-top: 1em;
+    color: #6c6f85;
+    font-weight: 600;
+}
+
+QGroupBox::title {
+    subcontrol-origin: margin;
+    left: 10px;
+    padding: 0 4px;
+}
+
+/* ── Progress bar ────────────────────────────────────────────────────────── */
+QProgressBar {
+    background-color: #ccd0da;
+    border: 1px solid #bcc0cc;
+    border-radius: 6px;
+    height: 10px;
+    text-align: center;
+}
+
+QProgressBar::chunk {
+    background-color: #1e66f5;
+    border-radius: 5px;
+}
+
+/* ── Dock widget ─────────────────────────────────────────────────────────── */
+QDockWidget {
+    color: #4c4f69;
+    titlebar-close-icon: none;
+    font-weight: 600;
+}
+
+QDockWidget::title {
+    background-color: #e6e9ef;
+    padding: 6px;
+    border-bottom: 1px solid #ccd0da;
+}
+
+/* ── Tool button ─────────────────────────────────────────────────────────── */
+QToolButton {
+    background-color: #ccd0da;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    border-radius: 5px;
+    padding: 4px 8px;
+    font-size: 13pt;
+}
+
+QToolButton:hover {
+    background-color: #bcc0cc;
+}
+
+/* ── Message box ─────────────────────────────────────────────────────────── */
+QMessageBox {
+    background-color: #eff1f5;
+}
+
+QMessageBox QLabel {
+    color: #4c4f69;
+    font-size: 10pt;
+}
+
+/* ── Empty workspace label ───────────────────────────────────────────────── */
+#emptyLabel {
+    color: #acb0be;
+    font-size: 14pt;
+    line-height: 2;
+}
+
+/* ── Status label in results toolbar ────────────────────────────────────── */
+#statusLabel {
+    color: #6c6f85;
+    font-size: 9pt;
+    padding-left: 4px;
+}
+
+/* ── DB label in SQL editor toolbar ─────────────────────────────────────── */
+#dbLabel {
+    color: #9ca0b0;
+    font-size: 9pt;
+    padding-right: 4px;
+}
+
+/* ── Workspace tab widget ────────────────────────────────────────────────── */
+#workspace > QTabBar::tab {
+    min-width: 120px;
+}
+
+/* ── Horizontal separator line in dialog ────────────────────────────────── */
+QFrame[frameShape="4"] {   /* HLine */
+    color: #ccd0da;
+    margin: 4px 0;
+}
+
+/* ── Structure view title ────────────────────────────────────────────────── */
+#structureTitle {
+    color: #7287fd;
+}
+
+/* ── Pagination bar ──────────────────────────────────────────────────────── */
+#paginationBar {
+    background-color: #e6e9ef;
+    border-top: 1px solid #bcc0cc;
+    min-height: 38px;
+}
+
+#pgBtn {
+    background-color: #d0d4de;
+    color: #4c4f69;
+    border: 1px solid #bcc0cc;
+    border-radius: 5px;
+    padding: 4px 10px;
+    font-size: 9pt;
+    min-width: 52px;
+}
+
+#pgBtn:hover {
+    background-color: #ccd0da;
+    border-color: #acb0be;
+}
+
+#pgBtn:disabled {
+    color: #bcc0cc;
+    background-color: #eff1f5;
+    border-color: #ccd0da;
+}
+
+#pageLbl {
+    color: #1e66f5;
+    font-size: 9pt;
+    font-weight: 600;
+    padding: 0 6px;
+}
+
+#rowCountLbl {
+    color: #6c6f85;
+    font-size: 9pt;
+    padding-left: 8px;
+}