feat: add BlockVariant for named widget block styles

demo/macos/Podfile.lock

@@ -1,15 +1,27 @@
 PODS:
   - FlutterMacOS (1.0.0)
+  - irondash_engine_context (0.0.1):
+    - FlutterMacOS
+  - super_native_extensions (0.0.1):
+    - FlutterMacOS
 
 DEPENDENCIES:
   - FlutterMacOS (from `Flutter/ephemeral`)
+  - irondash_engine_context (from `Flutter/ephemeral/.symlinks/plugins/irondash_engine_context/macos`)
+  - super_native_extensions (from `Flutter/ephemeral/.symlinks/plugins/super_native_extensions/macos`)
 
 EXTERNAL SOURCES:
   FlutterMacOS:
     :path: Flutter/ephemeral
+  irondash_engine_context:
+    :path: Flutter/ephemeral/.symlinks/plugins/irondash_engine_context/macos
+  super_native_extensions:
+    :path: Flutter/ephemeral/.symlinks/plugins/super_native_extensions/macos
 
 SPEC CHECKSUMS:
   FlutterMacOS: d0db08ddef1a9af05a5ec4b724367152bb0500b1
+  irondash_engine_context: 893c7d96d20ce361d7e996f39d360c4c2f9869ba
+  super_native_extensions: c2795d6d9aedf4a79fae25cb6160b71b50549189
 
 PODFILE CHECKSUM: 9ebaf0ce3d369aaa26a9ea0e159195ed94724cf3
 

demo/macos/Runner.xcodeproj/project.pbxproj

@@ -244,6 +244,7 @@
 				33CC10EB2044A3C60003C045 /* Resources */,
 				33CC110E2044A8840003C045 /* Bundle Framework */,
 				3399D490228B24CF009A79C7 /* ShellScript */,
+				8A14AB4F804B7CAA2E64DF2E /* [CP] Embed Pods Frameworks */,
 			);
 			buildRules = (
 			);
@@ -392,6 +393,23 @@
 			shellPath = /bin/sh;
 			shellScript = "\"$FLUTTER_ROOT\"/packages/flutter_tools/bin/macos_assemble.sh && touch Flutter/ephemeral/tripwire";
 		};
+		8A14AB4F804B7CAA2E64DF2E /* [CP] Embed Pods Frameworks */ = {
+			isa = PBXShellScriptBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+			);
+			inputFileListPaths = (
+				"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-frameworks-${CONFIGURATION}-input-files.xcfilelist",
+			);
+			name = "[CP] Embed Pods Frameworks";
+			outputFileListPaths = (
+				"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-frameworks-${CONFIGURATION}-output-files.xcfilelist",
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+			shellPath = /bin/sh;
+			shellScript = "\"${PODS_ROOT}/Target Support Files/Pods-Runner/Pods-Runner-frameworks.sh\"\n";
+			showEnvVarsInLog = 0;
+		};
 		E1EAB9F2FA8DCA9689F733BC /* [CP] Check Pods Manifest.lock */ = {
 			isa = PBXShellScriptBuildPhase;
 			buildActionMask = 2147483647;

docs/reference/deck-options.mdx

@@ -34,6 +34,57 @@ DeckOptions(
 )
 ```
 
+#### Named widget block styles
+
+Use `BlockVariant` in a `SlideStyle` stylesheet to target every named widget
+block with an exact, case-sensitive name. The selector applies to the block
+container and its complete widget subtree, so container spacing and descendant
+Mix styles resolve together.
+
+```dart
+import 'package:mix/mix.dart';
+import 'package:superdeck/superdeck.dart';
+
+const webviewBlock = BlockVariant('webview');
+
+final options = DeckOptions(
+  baseStyle: SlideStyle(
+    blockContainer: BoxStyler(
+      padding: EdgeInsetsGeometryMix.all(40),
+    ).variants([
+      VariantStyle(
+        webviewBlock,
+        BoxStyler(padding: EdgeInsetsGeometryMix.all(0)),
+      ),
+    ]),
+  ),
+);
+```
+
+`BlockVariant('webview')` matches both `@webview` and `@widget` blocks whose
+`name` is `webview`. Custom shorthand annotations work the same way, so
+`@chart` matches `BlockVariant('chart')`. The matching rule uses normal Mix
+precedence after the base style, and its margin and padding are included when
+SuperDeck calculates the child widget's usable size.
+
+SuperDeck already ships this exact zero padding and margin rule for `@webview`
+blocks by default, so a webview renders edge-to-edge without any stylesheet. The
+example above therefore doubles as the pattern for giving any other named block
+its own spacing.
+
+Only `WidgetBlock` names are selectable. Content blocks and section containers
+are not selectable; there are no per-instance IDs, classes, attributes, or
+selector composition. A plain `NamedVariant('image')` remains a manual Mix
+variant and is not activated merely because an `@image` block is rendered.
+Every widget block with the same name receives the same rule. Hardcoded styling
+inside a custom widget is unchanged unless that widget declares Mix styles that
+can respond to the inherited `BlockVariant`.
+
+Fullscreen layout does not create a separate block selector. It only removes
+header and footer chrome, so the same `BlockVariant('webview')` rule applies to
+normal and fullscreen WebView blocks; those two layouts cannot receive
+different rules based on `BlockVariant` alone.
+
 ### `styles`
 **Type:** `Map<String, SlideStyle>` | **Default:** `{}`
 

docs/reference/markdown-syntax.mdx

@@ -44,6 +44,18 @@ SuperDeck supports three core block types.
 
 Built-in widgets (`image`, `dartpad`, `webview`, `qrcode`) use the same widget syntax as `@widget`.
 
+### Styling named widget blocks
+
+Widget names can be selected from Dart stylesheets with `BlockVariant`. For
+example, `@webview` and the equivalent `@widget { name: "webview" }` both
+match `BlockVariant('webview')`; `@chart` matches `BlockVariant('chart')`.
+Matching is exact and case-sensitive.
+
+The selector affects the widget block container and descendants in that widget
+subtree. It does not select `@block`, `@section`, individual block instances,
+or arbitrary `NamedVariant` values. See the [DeckOptions reference](/reference/deck-options#named-widget-block-styles)
+for the stylesheet declaration and limitations.
+
 ## Common block properties
 
 ### `flex`

packages/superdeck/CHANGELOG.md

@@ -1,7 +1,10 @@
 ## Unreleased
 
-- Support `layout: fullscreen` slides, which suppress resolved headers and
-  footers while preserving the resolved background and style.
+- Add `BlockVariant` for opt-in, name-based `WidgetBlock` styling in Dart
+  stylesheets.
+- Render `@webview` blocks edge-to-edge (zero padding and margin) by default.
+- Always paint an opaque slide background so background-less slides no longer
+  bleed adjacent slides through during transitions.
 - Export `FileDeckLoader` and `BundledDeckLoader` from the public barrel so
   apps can use `SuperDeckApp.deckLoader` without importing from `src/`.
 - Fall back to bundled deck assets when auto-selection cannot discover a

packages/superdeck/lib/src/rendering/blocks/block_widget.dart

@@ -6,6 +6,7 @@ import 'package:mix/mix.dart';
 import 'package:superdeck_core/superdeck_core.dart';
 
 import '../../deck/slide_configuration.dart';
+import '../../styling/block_variant.dart';
 import '../../styling/components/slide.dart';
 import '../../ui/widgets/error_widgets.dart';
 import '../../ui/widgets/overflow_clip.dart';
@@ -39,8 +40,12 @@ class _BlockContainer extends StatefulWidget {
 class _BlockContainerState extends State<_BlockContainer> {
   @override
   Widget build(context) {
-    // Get the resolved SlideSpec (provided by SlideView)
-    final spec = SlideSpec.of(context);
+    // Widget blocks resolve their style inside [BlockVariantScope] so a named
+    // block variant affects both the rendered container and its child size.
+    final spec = switch (widget.block) {
+      WidgetBlock() => widget.configuration.style.resolve(context).spec,
+      ContentBlock() => SlideSpec.of(context),
+    };
 
     final blockOffset = spec.blockContainer.spec.calculateBlockOffset;
 
@@ -204,12 +209,15 @@ class CustomBlockWidget extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return _BlockContainer(
-      block: block,
-      size: size,
-      configuration: configuration,
-      runtimeKey: runtimeKey,
-      child: _CustomBlockChild(block: block),
+    return BlockVariantScope(
+      name: block.name,
+      child: _BlockContainer(
+        block: block,
+        size: size,
+        configuration: configuration,
+        runtimeKey: runtimeKey,
+        child: _CustomBlockChild(block: block),
+      ),
     );
   }
 }

packages/superdeck/lib/src/rendering/slides/slide_view.dart

@@ -101,6 +101,12 @@ class SlideView extends StatelessWidget {
       size: kResolution,
       child: Stack(
         children: [
+          // Opaque floor so a slide is never transparent: a transparent or
+          // absent background part would otherwise let other slides bleed
+          // through during cross-fade transitions.
+          const Positioned.fill(
+            child: ColoredBox(color: kSlideBackgroundColor),
+          ),
           // Background fills entire viewport (not affected by modifier)
           Positioned.fill(child: backgroundWidget),
           // Content wrapped with StyleBuilder to apply modifiers

packages/superdeck/lib/src/styling/block_variant.dart

@@ -0,0 +1,57 @@
+import 'package:flutter/widgets.dart';
+import 'package:mix/mix.dart';
+
+/// A Mix context selector for a named widget-block container and subtree.
+///
+/// A block variant is active only while building a widget block whose resolved
+/// name exactly matches [name].
+final class BlockVariant extends ContextVariant {
+  /// The widget block name this variant matches.
+  final String name;
+
+  const BlockVariant(this.name) : super('block_$name', _neverMatches);
+
+  @override
+  bool Function(BuildContext) get shouldApply => when;
+
+  @override
+  bool when(BuildContext context) {
+    return BlockVariantScope.maybeOf(context)?.name == name;
+  }
+
+  @override
+  bool operator ==(Object other) {
+    return identical(this, other) ||
+        other is BlockVariant && other.name == name;
+  }
+
+  @override
+  int get hashCode => name.hashCode;
+}
+
+bool _neverMatches(BuildContext _) => false;
+
+/// Provides the current named widget block to descendants.
+///
+/// This scope is used by SuperDeck's renderer. It is intentionally not
+/// exported from the public package barrel.
+class BlockVariantScope extends InheritedWidget {
+  /// The resolved widget-block name for this subtree.
+  final String name;
+
+  const BlockVariantScope({
+    super.key,
+    required this.name,
+    required super.child,
+  });
+
+  /// Returns the nearest block variant scope, if one is active.
+  static BlockVariantScope? maybeOf(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<BlockVariantScope>();
+  }
+
+  @override
+  bool updateShouldNotify(BlockVariantScope oldWidget) {
+    return name != oldWidget.name;
+  }
+}

packages/superdeck/lib/src/styling/default_style.dart

@@ -3,6 +3,7 @@ import 'package:flutter/widgets.dart';
 import 'package:google_fonts/google_fonts.dart';
 import 'package:mix/mix.dart';
 
+import 'block_variant.dart';
 import 'components/markdown_alert.dart';
 import 'components/markdown_alert_type.dart';
 import 'components/markdown_blockquote.dart';
@@ -30,6 +31,11 @@ TextStyle get _baseTextStyle => _safeGoogleFont(
 const onGist = NamedVariant('gist');
 const onImage = NamedVariant('image');
 
+// A webview fills its own block, so it ships edge-to-edge by default. This uses
+// [BlockVariant] because a plain [NamedVariant] does not activate for a rendered
+// widget block; only [BlockVariant] reliably targets the `@webview` container.
+const onWebview = BlockVariant('webview');
+
 WidgetModifierConfig _pad(EdgeInsetsGeometryMix value) =>
     WidgetModifierConfig.padding(value);
 
@@ -230,6 +236,13 @@ SlideStyle _createDefaultSlideStyle() {
           margin: EdgeInsetsGeometryMix.all(0),
         ),
       ),
+      VariantStyle(
+        onWebview,
+        BoxStyler(
+          padding: EdgeInsetsGeometryMix.all(0),
+          margin: EdgeInsetsGeometryMix.all(0),
+        ),
+      ),
     ]),
 
     slideContainer: BoxStyler(),

packages/superdeck/lib/src/ui/app_shell.dart

@@ -274,7 +274,7 @@ class _SplitViewState extends State<SplitView>
         final buildFailure = deckController.session.buildFailure.value;
 
         return Scaffold(
-          backgroundColor: const Color.fromARGB(255, 9, 9, 9),
+          backgroundColor: kSlideBackgroundColor,
           floatingActionButtonLocation:
               FloatingActionButtonLocation.miniEndFloat,
           floatingActionButton: _buildFloatingAction(

packages/superdeck/lib/src/utils/constants.dart

@@ -8,5 +8,14 @@ const _kHeight = 720.0;
 
 const kResolution = Size(_kWidth, _kHeight);
 
+/// Opaque backdrop painted behind a slide when no background part is set.
+///
+/// Guarantees a slide is never transparent: without it, a background-less slide
+/// (e.g. a template with no chrome) would show through to whatever is behind it,
+/// which bleeds the outgoing/incoming slide through during cross-fade
+/// transitions. Matches the app shell letterbox so the default is invisible
+/// except during transitions.
+const kSlideBackgroundColor = Color(0xFF090909);
+
 const kIsTest = bool.fromEnvironment('FLUTTER_TEST');
 const kCanRunProcess = kDebugMode && !kIsWeb && !kIsTest;

packages/superdeck/lib/superdeck.dart

@@ -12,6 +12,7 @@ export 'src/thumbnails/async_thumbnail.dart';
 export 'src/thumbnails/thumbnail_service.dart';
 
 // Styling
+export 'src/styling/block_variant.dart' show BlockVariant;
 export 'src/styling/default_style.dart';
 export 'src/styling/components/markdown_alert.dart';
 export 'src/styling/components/markdown_alert_type.dart';