diff --git a/PLAN.md b/PLAN.md
index 4cb0c3b..d7d103b 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -1,4 +1,4 @@
-# SQLiteView 書き込み対応計画
+# SQLiteView 開発計画
 
 ## Context
 
@@ -83,3 +83,75 @@ SQLiteView は INSERT/UPDATE/DELETE/CREATE/DROP/BEGIN/COMMIT/ROLLBACK 等の書
   - `build_deb.sh`: `tomllib`（Python 3.11+）→ `grep`/`sed` に置換（Python 3.10互換性復元）
   - `_strip_sql_noise()`: ダブルクォート識別子の除去を追加（セキュリティ強化）
   - エラーパステスト6件追加（空クエリ、無効SQL、未接続操作、存在しないファイル、文字列リテラル内WHERE）
+
+---
+
+## フェーズ2: UI/UX 改善（完了）
+
+### Context
+
+機能は十分だが、UIスタイリングが一切なくシステムネイティブテーマのまま。ダークモード非対応、SQLエディタのフォント未指定、ショートカットも最低限(Ctrl+O/Q のみ)。開発者ツールとしての使い勝手を底上げする。
+
+### 変更対象ファイル
+
+**新規作成:**
+- `src/sqliteviewer/theme.py` — Theme enum, QSS読み込み/適用/永続化 (~60行)
+- `src/sqliteviewer/resources/light.qss` — ライトテーマ QSS (~180行)
+- `src/sqliteviewer/resources/dark.qss` — ダークテーマ QSS (~180行)
+
+**変更:**
+- `src/sqliteviewer/app.py` — 起動時テーマ適用 (+3行)
+- `src/sqliteviewer/mainwindow.py` — View メニュー、テーマ切替、フォント、ショートカット (+~40行)
+- `src/sqliteviewer/sql_highlighter.py` — テーマ連動カラースキーム追加 (+~25行)
+
+### Step 5: テーマ基盤 + ダークモード（完了）
+
+- [x] `theme.py` を作成 — `Theme` enum (LIGHT/DARK)、`load_theme()`/`apply_theme()`/`save_theme_preference()`/`load_theme_preference()`
+  > `StrEnum`(3.11+) → `str, Enum`(3.10+) に修正済み（`requires-python >= 3.10` 互換）
+- [x] `light.qss` を作成 — GitHub風パレット (bg `#ffffff`, fg `#24292e`, accent `#0366d6`)
+  - 対象: QMainWindow, QTableView, QTabWidget, QListWidget, QPlainTextEdit, QTextEdit, QPushButton, QSplitter, QMenuBar, QMenu, QStatusBar, QScrollBar, QHeaderView
+  - ボタン hover/pressed 効果、タブ選択インジケーター、スリムスクロールバー、角丸4px
+- [x] `dark.qss` を作成 — VS Code dark 風パレット (bg `#1e1e1e`, fg `#d4d4d4`, accent `#4fc1ff`)
+- [x] `app.py` を変更 — `window.show()` 前に `apply_theme(load_theme_preference())` を呼ぶ
+- [x] `mainwindow.py` に View メニュー追加 — "Toggle Dark Mode" (Ctrl+D)
+- [x] `sql_highlighter.py` に `set_color_scheme()` 追加 — ライト (GitHub風) / ダーク (VS Code風) の2パレットを切替、`rehighlight()` で即反映
+- [x] `mainwindow.py` でハイライター参照を保持し、テーマ切替時に色同期
+  > テーマ設定は `QSettings("SQLiteViewer", "App")` の `theme` キーへ保存し、起動時に `app.py` で先に適用する。
+
+### Step 6: モノスペースフォント（完了）
+
+- [x] `QFontDatabase.systemFont(SystemFont.FixedFont)` でモノスペースフォント取得、11pt
+- [x] `query_editor` と `schema_view` に適用
+- [x] フォント設定後に `setTabStopDistance` を再計算
+
+### Step 7: キーボードショートカット（完了）
+
+- [x] `Ctrl+Enter` / `F5` — クエリ実行 (`QShortcut` で query_editor にバインド)
+- [x] `Ctrl+R` — テーブルリフレッシュ (View メニューにアクション追加)
+- [x] Run Query ボタンにツールチップ `"Execute SQL (Ctrl+Enter)"` 追加
+
+### 設計判断
+
+- **QSS方式** — QPaletteより柔軟 (hover/角丸/スクロールバー)、外部ライブラリ不要
+- **テーマ2種のみ** — Light/Dark。レジストリパターンは over-engineering
+- **QFontDatabase.systemFont** — フォント名ハードコードより確実なクロスプラットフォーム対応
+- **QShortcut** — eventFilter やサブクラス化より軽量
+
+### 検証方法
+
+```bash
+# 回帰テスト
+uv run python -m pytest tests/ -v
+
+# 手動テスト
+uv run python -m sqliteviewer
+# → View > Toggle Dark Mode で切替確認
+# → SQLエディタがモノスペースフォントか確認
+# → Ctrl+Enter / F5 でクエリ実行確認
+# → Ctrl+R でテーブルリフレッシュ確認
+# → アプリ再起動後にテーマ維持されるか確認
+```
+
+## 現状
+
+フェーズ2まで実装済み。SQLiteView はライト/ダークテーマ切替、固定幅フォントの SQL エディタ/スキーマ表示、`Ctrl+Enter`・`F5`・`Ctrl+R` の操作に対応した。レビューで `StrEnum`(3.11+) の Python 3.10 非互換を検出し `str, Enum` に修正済み。
diff --git a/src/sqliteviewer/app.py b/src/sqliteviewer/app.py
index 3a1fa09..a5ac2e4 100644
--- a/src/sqliteviewer/app.py
+++ b/src/sqliteviewer/app.py
@@ -9,6 +9,7 @@
 from PyQt6.QtWidgets import QApplication
 
 from .mainwindow import MainWindow
+from .theme import apply_theme, load_theme_preference
 
 
 def run(initial_path: Optional[str] = None) -> int:
@@ -22,6 +23,7 @@ def run(initial_path: Optional[str] = None) -> int:
         app.setOrganizationName("SQLiteView")
         owns_app = True
 
+    apply_theme(load_theme_preference(), app)
     window = MainWindow()
     window.show()
 
diff --git a/src/sqliteviewer/mainwindow.py b/src/sqliteviewer/mainwindow.py
index 1fbe070..e474a61 100644
--- a/src/sqliteviewer/mainwindow.py
+++ b/src/sqliteviewer/mainwindow.py
@@ -7,7 +7,7 @@
 from typing import Optional
 
 from PyQt6.QtCore import QSettings, Qt
-from PyQt6.QtGui import QAction, QCloseEvent
+from PyQt6.QtGui import QAction, QCloseEvent, QFontDatabase, QKeySequence, QShortcut
 from PyQt6.QtWidgets import (
     QApplication,
     QFileDialog,
@@ -32,6 +32,7 @@
 from .database import DatabaseError, DatabaseService, QueryResult
 from .resources import load_icon
 from .sql_highlighter import SqlHighlighter
+from .theme import SETTINGS_GROUP, Theme, apply_theme, load_theme_preference, save_theme_preference
 
 
 MAX_RECENT_FILES = 5
@@ -47,8 +48,9 @@ def __init__(self) -> None:
         self.setWindowIcon(load_icon())
 
         self.database_service = DatabaseService()
-        self.settings = QSettings("SQLiteViewer", "App")
+        self.settings = QSettings(*SETTINGS_GROUP)
         self.query_result: Optional[QueryResult] = None
+        self.current_theme = load_theme_preference()
 
         self.table_list = QListWidget()
         self.table_list.itemSelectionChanged.connect(self._on_table_selected)
@@ -64,8 +66,16 @@ def __init__(self) -> None:
 
         self.query_editor = QPlainTextEdit()
         self.query_editor.setPlaceholderText("Write a SQL statement…")
-        self.query_editor.setTabStopDistance(4 * self.query_editor.fontMetrics().horizontalAdvance(' '))
-        SqlHighlighter(self.query_editor.document())
+        self.highlighter = SqlHighlighter(self.query_editor.document())
+        self.highlighter.set_color_scheme(self.current_theme)
+
+        fixed_font = QFontDatabase.systemFont(QFontDatabase.SystemFont.FixedFont)
+        fixed_font.setPointSize(11)
+        self.query_editor.setFont(fixed_font)
+        self.schema_view.setFont(fixed_font)
+        tab_stop = 4 * self.query_editor.fontMetrics().horizontalAdvance(" ")
+        self.query_editor.setTabStopDistance(tab_stop)
+        self.schema_view.setTabStopDistance(tab_stop)
 
         self.query_result_view = QTableView()
         self.query_result_view.setSelectionBehavior(QTableView.SelectionBehavior.SelectRows)
@@ -117,11 +127,12 @@ def _build_ui(self) -> None:
         query_layout.addWidget(self.query_editor)
 
         button_bar = QHBoxLayout()
-        run_button = QPushButton("Run Query")
-        run_button.clicked.connect(self._run_query)
+        self.run_button = QPushButton("Run Query")
+        self.run_button.setToolTip("Execute SQL (Ctrl+Enter)")
+        self.run_button.clicked.connect(self._run_query)
         export_button = QPushButton("Export Results")
         export_button.clicked.connect(self._export_results)
-        button_bar.addWidget(run_button)
+        button_bar.addWidget(self.run_button)
         button_bar.addWidget(export_button)
         button_bar.addStretch(1)
         query_layout.addLayout(button_bar)
@@ -159,16 +170,46 @@ def _build_menus(self) -> None:
         exit_action.triggered.connect(QApplication.instance().quit)
         file_menu.addAction(exit_action)
 
+        view_menu = menubar.addMenu("&View")
+
+        self.toggle_dark_mode_action = QAction("Toggle Dark Mode", self)
+        self.toggle_dark_mode_action.setShortcut("Ctrl+D")
+        self.toggle_dark_mode_action.setCheckable(True)
+        self.toggle_dark_mode_action.setChecked(self.current_theme == Theme.DARK)
+        self.toggle_dark_mode_action.toggled.connect(self._toggle_dark_mode)
+        view_menu.addAction(self.toggle_dark_mode_action)
+
+        refresh_action = QAction("Refresh Tables", self)
+        refresh_action.setShortcut("Ctrl+R")
+        refresh_action.triggered.connect(self._refresh_tables)
+        view_menu.addAction(refresh_action)
+
         help_menu = menubar.addMenu("&Help")
         about_action = QAction("About", self)
         about_action.triggered.connect(self._show_about_dialog)
         help_menu.addAction(about_action)
 
+        self._install_shortcuts()
+
+    def _install_shortcuts(self) -> None:
+        for shortcut_key in ("Ctrl+Return", "Ctrl+Enter", "F5"):
+            shortcut = QShortcut(QKeySequence(shortcut_key), self.query_editor)
+            shortcut.activated.connect(self._run_query)
+
     def _open_dialog(self) -> None:
         path, _ = QFileDialog.getOpenFileName(self, "Open SQLite Database", str(Path.home()), "SQLite Database (*.db *.sqlite *.sqlite3);;All Files (*)")
         if path:
             self.open_database(path)
 
+    def _toggle_dark_mode(self, checked: bool) -> None:
+        self._set_theme(Theme.DARK if checked else Theme.LIGHT)
+
+    def _set_theme(self, theme: Theme) -> None:
+        self.current_theme = theme
+        apply_theme(theme)
+        save_theme_preference(theme)
+        self.highlighter.set_color_scheme(theme)
+
     def open_database(self, path: str) -> None:
         try:
             self.database_service.open(path)
diff --git a/src/sqliteviewer/resources/dark.qss b/src/sqliteviewer/resources/dark.qss
new file mode 100644
index 0000000..79df5af
--- /dev/null
+++ b/src/sqliteviewer/resources/dark.qss
@@ -0,0 +1,154 @@
+QMainWindow, QWidget {
+    background-color: #1e1e1e;
+    color: #d4d4d4;
+}
+
+QStatusBar {
+    background-color: #252526;
+    color: #9da3a9;
+    border-top: 1px solid #333333;
+}
+
+QMenuBar {
+    background-color: #252526;
+    color: #d4d4d4;
+    border-bottom: 1px solid #333333;
+}
+
+QMenuBar::item {
+    padding: 6px 10px;
+    background: transparent;
+}
+
+QMenuBar::item:selected,
+QMenu::item:selected {
+    background-color: #09395a;
+    color: #ffffff;
+    border-radius: 4px;
+}
+
+QMenu {
+    background-color: #252526;
+    color: #d4d4d4;
+    border: 1px solid #333333;
+    padding: 6px;
+}
+
+QMenu::item {
+    padding: 6px 22px 6px 10px;
+    margin: 2px 0;
+}
+
+QMenu::separator {
+    height: 1px;
+    background: #333333;
+    margin: 6px 0;
+}
+
+QListWidget,
+QTableView,
+QPlainTextEdit,
+QTextEdit {
+    background-color: #1e1e1e;
+    color: #d4d4d4;
+    border: 1px solid #333333;
+    border-radius: 4px;
+    selection-background-color: #264f78;
+    selection-color: #ffffff;
+    gridline-color: #2d2d30;
+}
+
+QPlainTextEdit,
+QTextEdit {
+    background-color: #1b1b1c;
+}
+
+QHeaderView::section {
+    background-color: #252526;
+    color: #c5c5c5;
+    border: none;
+    border-bottom: 1px solid #333333;
+    border-right: 1px solid #2d2d30;
+    padding: 6px 8px;
+}
+
+QPushButton {
+    background-color: #2d2d30;
+    color: #d4d4d4;
+    border: 1px solid #3f3f46;
+    border-radius: 4px;
+    padding: 6px 12px;
+}
+
+QPushButton:hover {
+    background-color: #35353a;
+    border-color: #4fc1ff;
+}
+
+QPushButton:pressed {
+    background-color: #41414a;
+}
+
+QTabWidget::pane {
+    border: 1px solid #333333;
+    border-radius: 4px;
+    top: -1px;
+}
+
+QTabBar::tab {
+    background-color: #252526;
+    color: #9da3a9;
+    padding: 8px 14px;
+    margin-right: 4px;
+    border-top-left-radius: 4px;
+    border-top-right-radius: 4px;
+}
+
+QTabBar::tab:selected {
+    background-color: #1e1e1e;
+    color: #ffffff;
+    border-bottom: 2px solid #4fc1ff;
+}
+
+QTabBar::tab:hover:!selected {
+    background-color: #2d2d30;
+}
+
+QSplitter::handle {
+    background-color: #333333;
+    width: 2px;
+    height: 2px;
+}
+
+QScrollBar:vertical {
+    background: transparent;
+    width: 10px;
+    margin: 2px;
+}
+
+QScrollBar:horizontal {
+    background: transparent;
+    height: 10px;
+    margin: 2px;
+}
+
+QScrollBar::handle:vertical,
+QScrollBar::handle:horizontal {
+    background: #4a4a4f;
+    border-radius: 4px;
+    min-height: 24px;
+    min-width: 24px;
+}
+
+QScrollBar::handle:vertical:hover,
+QScrollBar::handle:horizontal:hover {
+    background: #5a5a60;
+}
+
+QScrollBar::add-line,
+QScrollBar::sub-line,
+QScrollBar::add-page,
+QScrollBar::sub-page {
+    background: none;
+    border: none;
+}
diff --git a/src/sqliteviewer/resources/light.qss b/src/sqliteviewer/resources/light.qss
new file mode 100644
index 0000000..ea32b87
--- /dev/null
+++ b/src/sqliteviewer/resources/light.qss
@@ -0,0 +1,154 @@
+QMainWindow, QWidget {
+    background-color: #ffffff;
+    color: #24292e;
+}
+
+QStatusBar {
+    background-color: #f6f8fa;
+    color: #586069;
+    border-top: 1px solid #d0d7de;
+}
+
+QMenuBar {
+    background-color: #f6f8fa;
+    color: #24292e;
+    border-bottom: 1px solid #d0d7de;
+}
+
+QMenuBar::item {
+    padding: 6px 10px;
+    background: transparent;
+}
+
+QMenuBar::item:selected,
+QMenu::item:selected {
+    background-color: #ddf4ff;
+    color: #24292e;
+    border-radius: 4px;
+}
+
+QMenu {
+    background-color: #ffffff;
+    color: #24292e;
+    border: 1px solid #d0d7de;
+    padding: 6px;
+}
+
+QMenu::item {
+    padding: 6px 22px 6px 10px;
+    margin: 2px 0;
+}
+
+QMenu::separator {
+    height: 1px;
+    background: #d8dee4;
+    margin: 6px 0;
+}
+
+QListWidget,
+QTableView,
+QPlainTextEdit,
+QTextEdit {
+    background-color: #ffffff;
+    color: #24292e;
+    border: 1px solid #d0d7de;
+    border-radius: 4px;
+    selection-background-color: #c8e1ff;
+    selection-color: #24292e;
+    gridline-color: #eaeef2;
+}
+
+QPlainTextEdit,
+QTextEdit {
+    background-color: #fdfefe;
+}
+
+QHeaderView::section {
+    background-color: #f6f8fa;
+    color: #57606a;
+    border: none;
+    border-bottom: 1px solid #d0d7de;
+    border-right: 1px solid #eaeef2;
+    padding: 6px 8px;
+}
+
+QPushButton {
+    background-color: #f6f8fa;
+    color: #24292e;
+    border: 1px solid #d0d7de;
+    border-radius: 4px;
+    padding: 6px 12px;
+}
+
+QPushButton:hover {
+    background-color: #eef2f6;
+    border-color: #afb8c1;
+}
+
+QPushButton:pressed {
+    background-color: #e1e4e8;
+}
+
+QTabWidget::pane {
+    border: 1px solid #d0d7de;
+    border-radius: 4px;
+    top: -1px;
+}
+
+QTabBar::tab {
+    background-color: #f6f8fa;
+    color: #57606a;
+    padding: 8px 14px;
+    margin-right: 4px;
+    border-top-left-radius: 4px;
+    border-top-right-radius: 4px;
+}
+
+QTabBar::tab:selected {
+    background-color: #ffffff;
+    color: #24292e;
+    border-bottom: 2px solid #0366d6;
+}
+
+QTabBar::tab:hover:!selected {
+    background-color: #eef2f6;
+}
+
+QSplitter::handle {
+    background-color: #eaeef2;
+    width: 2px;
+    height: 2px;
+}
+
+QScrollBar:vertical {
+    background: transparent;
+    width: 10px;
+    margin: 2px;
+}
+
+QScrollBar:horizontal {
+    background: transparent;
+    height: 10px;
+    margin: 2px;
+}
+
+QScrollBar::handle:vertical,
+QScrollBar::handle:horizontal {
+    background: #c1c7cd;
+    border-radius: 4px;
+    min-height: 24px;
+    min-width: 24px;
+}
+
+QScrollBar::handle:vertical:hover,
+QScrollBar::handle:horizontal:hover {
+    background: #959da5;
+}
+
+QScrollBar::add-line,
+QScrollBar::sub-line,
+QScrollBar::add-page,
+QScrollBar::sub-page {
+    background: none;
+    border: none;
+}
diff --git a/src/sqliteviewer/sql_highlighter.py b/src/sqliteviewer/sql_highlighter.py
index bd4e85b..822b3f4 100644
--- a/src/sqliteviewer/sql_highlighter.py
+++ b/src/sqliteviewer/sql_highlighter.py
@@ -5,10 +5,27 @@
 from PyQt6.QtCore import QRegularExpression
 from PyQt6.QtGui import QColor, QFont, QTextCharFormat, QSyntaxHighlighter
 
+from .theme import Theme
+
 
 class SqlHighlighter(QSyntaxHighlighter):
     """Applies formatting rules to highlight SQL keywords and tokens."""
 
+    COLOR_SCHEMES = {
+        Theme.LIGHT: {
+            "keyword": "#005cc5",
+            "comment": "#6a737d",
+            "string": "#22863a",
+            "number": "#b31d28",
+        },
+        Theme.DARK: {
+            "keyword": "#4fc1ff",
+            "comment": "#6a9955",
+            "string": "#ce9178",
+            "number": "#b5cea8",
+        },
+    }
+
     KEYWORDS = {
         # Read / query
         "SELECT",
@@ -109,18 +126,14 @@ class SqlHighlighter(QSyntaxHighlighter):
     def __init__(self, document) -> None:
         super().__init__(document)
         self.keyword_format = QTextCharFormat()
-        self.keyword_format.setForeground(QColor("#005cc5"))
         self.keyword_format.setFontWeight(QFont.Weight.Bold)
 
         self.comment_format = QTextCharFormat()
-        self.comment_format.setForeground(QColor("#6a737d"))
         self.comment_format.setFontItalic(True)
 
         self.string_format = QTextCharFormat()
-        self.string_format.setForeground(QColor("#22863a"))
 
         self.number_format = QTextCharFormat()
-        self.number_format.setForeground(QColor("#b31d28"))
 
         self.comment_expression = QRegularExpression(r"--[^\n]*")
         self.string_expression = QRegularExpression(r"'([^']|'')*'")
@@ -129,6 +142,17 @@ def __init__(self, document) -> None:
         pattern_str = r"\b(" + "|".join(self.KEYWORDS) + r")\b"
         self.keyword_pattern = QRegularExpression(pattern_str)
         self.keyword_pattern.setPatternOptions(QRegularExpression.PatternOption.CaseInsensitiveOption)
+        self.set_color_scheme(Theme.LIGHT)
+
+    def set_color_scheme(self, theme: Theme) -> None:
+        """Update token colors for the selected theme."""
+
+        colors = self.COLOR_SCHEMES[theme]
+        self.keyword_format.setForeground(QColor(colors["keyword"]))
+        self.comment_format.setForeground(QColor(colors["comment"]))
+        self.string_format.setForeground(QColor(colors["string"]))
+        self.number_format.setForeground(QColor(colors["number"]))
+        self.rehighlight()
 
     def highlightBlock(self, text: str) -> None:  # noqa: N802 (Qt API signature)
         self._apply_regex(self.keyword_pattern, text, self.keyword_format)
diff --git a/src/sqliteviewer/theme.py b/src/sqliteviewer/theme.py
new file mode 100644
index 0000000..7777846
--- /dev/null
+++ b/src/sqliteviewer/theme.py
@@ -0,0 +1,59 @@
+"""Theme helpers for the SQLite viewer."""
+
+from __future__ import annotations
+
+from enum import Enum
+
+from PyQt6.QtCore import QSettings
+from PyQt6.QtWidgets import QApplication
+
+from .resources import resource_path
+
+
+class Theme(str, Enum):
+    """Supported application themes."""
+
+    LIGHT = "light"
+    DARK = "dark"
+
+
+SETTINGS_GROUP = ("SQLiteViewer", "App")
+_THEME_KEY = "theme"
+
+
+def load_theme(theme: Theme) -> str:
+    """Load the QSS content for the requested theme."""
+
+    stylesheet_path = resource_path(f"{theme.value}.qss")
+    with open(stylesheet_path, encoding="utf-8") as stylesheet_file:
+        return stylesheet_file.read()
+
+
+def apply_theme(theme: Theme, app: QApplication | None = None) -> Theme:
+    """Apply the requested theme to the current application."""
+
+    current_app = app or QApplication.instance()
+    if current_app is None:
+        raise RuntimeError("QApplication must exist before applying a theme.")
+
+    current_app.setStyleSheet(load_theme(theme))
+    current_app.setProperty("theme", theme.value)
+    return theme
+
+
+def save_theme_preference(theme: Theme) -> None:
+    """Persist the theme preference."""
+
+    settings = QSettings(*SETTINGS_GROUP)
+    settings.setValue(_THEME_KEY, theme.value)
+
+
+def load_theme_preference() -> Theme:
+    """Load the persisted theme preference."""
+
+    settings = QSettings(*SETTINGS_GROUP)
+    stored_theme = settings.value(_THEME_KEY, Theme.LIGHT.value, type=str)
+    try:
+        return Theme(stored_theme)
+    except ValueError:
+        return Theme.LIGHT