Themes and test fixes. Reduce dependence on App.dark

src/textual/_text_area_theme.py

@@ -5,9 +5,7 @@
 
 from rich.style import Style
 
-from textual.app import DEFAULT_COLORS
 from textual.color import Color
-from textual.design import DEFAULT_DARK_SURFACE
 
 if TYPE_CHECKING:
     from textual.widgets import TextArea
@@ -92,9 +90,12 @@ def apply_css(self, text_area: TextArea) -> None:
         if self.base_style.color is None:
             self.base_style = Style(color="#f3f3f3", bgcolor=self.base_style.bgcolor)
 
+        app = text_area.app
+        app_theme = app.get_theme(app.theme)
+
         if self.base_style.bgcolor is None:
             self.base_style = Style(
-                color=self.base_style.color, bgcolor=DEFAULT_DARK_SURFACE
+                color=self.base_style.color, bgcolor=app_theme.surface
             )
 
         configured = self._theme_configured_attributes.__contains__
@@ -148,7 +149,7 @@ def apply_css(self, text_area: TextArea) -> None:
                 self.selection_style = selection_style
             else:
                 selection_background_color = background_color.blend(
-                    DEFAULT_COLORS["dark"].primary, factor=0.75
+                    app_theme.primary, factor=0.75
                 )
                 self.selection_style = Style.from_color(
                     bgcolor=selection_background_color.rich_color

src/textual/app.py

@@ -122,6 +122,7 @@
     SystemModalScreen,
 )
 from textual.signal import Signal
+from textual.theme import BUILTIN_THEMES, Theme
 from textual.timer import Timer
 from textual.widget import AwaitMount, Widget
 from textual.widgets._toast import ToastRack
@@ -187,6 +188,7 @@
     ),
 }
 
+
 ComposeResult = Iterable[Widget]
 RenderResult = RenderableType
 
@@ -544,6 +546,11 @@ def __init__(
         super().__init__()
         self.features: frozenset[FeatureFlag] = parse_features(os.getenv("TEXTUAL", ""))
 
+        self._registered_themes: dict[str, Theme] = {}
+        """Themes that have been registered with the App using `App.register_theme`.
+        
+        This excludes the built-in themes."""
+
         ansi_theme = self.ansi_theme_dark if self.dark else self.ansi_theme_light
         self.set_reactive(App.ansi_color, ansi_color)
         self._filters: list[LineFilter] = [
@@ -646,9 +653,10 @@ def __init__(
 
         self._refresh_required = False
 
-        self.design = DEFAULT_COLORS
-
         self._css_has_errors = False
+
+        # Note that the theme must be set *before* self.get_css_variables() is called
+        # to ensure that the variables are retrieved from the currently active theme.
         self.stylesheet = Stylesheet(variables=self.get_css_variables())
 
         css_path = css_path or self.CSS_PATH
@@ -898,8 +906,9 @@ def get_pseudo_classes(self) -> Iterable[str]:
         Returns:
             Names of the pseudo classes.
         """
+        app_theme = self.get_theme(self.theme)
         yield "focus" if self.app_focus else "blur"
-        yield "dark" if self.dark else "light"
+        yield "dark" if app_theme.dark else "light"
         if self.is_inline:
             yield "inline"
         if self.ansi_color:
@@ -1166,14 +1175,47 @@ def get_css_variables(self) -> dict[str, str]:
         Returns:
             A mapping of variable name to value.
         """
+        theme = self.get_theme(self.theme)
+        variables = theme.to_color_system().generate()
+        return variables
 
-        if self.dark:
-            design = self.design["dark"]
-        else:
-            design = self.design["light"]
+    def get_theme(self, theme_name: str) -> Theme:
+        """Get a theme by name.
 
-        variables = design.generate()
-        return variables
+        Args:
+            theme_name: The name of the theme to get.
+
+        Returns:
+            A Theme instance.
+        """
+        return self.available_themes[theme_name]
+
+    def register_theme(self, theme: Theme) -> None:
+        """Register a theme with the app.
+
+        A theme must be registered before it is set as the `App.theme`.
+
+        Args:
+            theme: The theme to register.
+        """
+        self._registered_themes[theme.name] = theme
+
+    @property
+    def available_themes(self) -> dict[str, Theme]:
+        """All available themes (all built-in themes plus any that have been registered)."""
+        return {**BUILTIN_THEMES, **self._registered_themes}
+
+    def watch_theme(self, theme_name: str) -> None:
+        """Apply a theme to the application.
+
+        This method is called when the theme reactive attribute is set.
+        """
+        theme = self.get_theme(theme_name)
+        dark = theme.dark
+        self.set_class(dark, "-dark-mode", update=False)
+        self.set_class(not dark, "-light-mode", update=False)
+        self._refresh_truecolor_filter(self.ansi_theme)
+        self.call_next(self.refresh_css)
 
     def watch_dark(self, dark: bool) -> None:
         """Watches the dark bool.
@@ -1187,12 +1229,14 @@ def watch_dark(self, dark: bool) -> None:
         self.call_next(self.refresh_css)
 
     def watch_ansi_theme_dark(self, theme: TerminalTheme) -> None:
-        if self.dark:
+        app_theme = self.get_theme(self.theme)
+        if app_theme.dark:
             self._refresh_truecolor_filter(theme)
             self.call_next(self.refresh_css)
 
     def watch_ansi_theme_light(self, theme: TerminalTheme) -> None:
-        if not self.dark:
+        app_theme = self.get_theme(self.theme)
+        if not app_theme.dark:
             self._refresh_truecolor_filter(theme)
             self.call_next(self.refresh_css)
 
@@ -1203,7 +1247,8 @@ def ansi_theme(self) -> TerminalTheme:
         Defines how colors defined as ANSI (e.g. `magenta`) inside Rich renderables
         are mapped to hex codes.
         """
-        return self.ansi_theme_dark if self.dark else self.ansi_theme_light
+        app_theme = self.get_theme(self.theme)
+        return self.ansi_theme_dark if app_theme.dark else self.ansi_theme_light
 
     def _refresh_truecolor_filter(self, theme: TerminalTheme) -> None:
         """Update the ANSI to Truecolor filter, if available, with a new theme mapping.