feat: default block alignment to centerLeft

docs/reference/block-types.mdx

@@ -13,13 +13,16 @@ Content and widget blocks support these properties. Sections support `align`
 and `flex`, but scrolling is configured on child blocks or widgets.
 
 ### `align`
-**Type:** String | **Default:** `center`
+**Type:** String | **Default:** `centerLeft`
 
 Controls content alignment:
 - `topLeft`, `topCenter`, `topRight`
 - `centerLeft`, `center`, `centerRight`
 - `bottomLeft`, `bottomCenter`, `bottomRight`
 
+Blocks default to `centerLeft` because paragraph-like content reads better
+left-aligned. Set `align: center` explicitly for titles or short callouts.
+
 ### `flex`
 **Type:** Number | **Default:** `1`
 

docs/reference/markdown-syntax.mdx

@@ -51,7 +51,7 @@ Built-in widgets (`image`, `dartpad`, `qrcode`) use the same widget syntax as `@
 ### `align`
 
 - Type: string
-- Default: `center`
+- Default: `centerLeft`
 - Values: `topLeft`, `topCenter`, `topRight`, `centerLeft`, `center`, `centerRight`, `bottomLeft`, `bottomCenter`, `bottomRight`
 
 ### `scrollable`

packages/core/lib/src/deck/block_model.dart

@@ -48,6 +48,14 @@ sealed class Block with BlockMappable {
   );
 
   static final fromMap = BlockMapper.fromMap;
+
+  /// The effective alignment for this block.
+  ///
+  /// When [align] is not set explicitly, defaults to
+  /// [ContentAlignment.centerLeft] because paragraph-like content is easier
+  /// to read and scan when left-aligned. Set `align: center` explicitly to
+  /// restore the previous default.
+  ContentAlignment get resolvedAlign => align ?? ContentAlignment.centerLeft;
 }
 
 /// A section that contains multiple child blocks arranged horizontally.

packages/core/test/src/deck/block_model_test.dart

@@ -287,6 +287,24 @@ void main() {
         expect(block.scrollable, true);
       });
 
+      group('resolvedAlign', () {
+        test('defaults to centerLeft when align is not set', () {
+          final block = ContentBlock('Content');
+
+          expect(block.align, isNull);
+          expect(block.resolvedAlign, ContentAlignment.centerLeft);
+        });
+
+        test('uses explicit align when set', () {
+          final block = ContentBlock(
+            'Content',
+            align: ContentAlignment.center,
+          );
+
+          expect(block.resolvedAlign, ContentAlignment.center);
+        });
+      });
+
       group('copyWith', () {
         test('copies with new content', () {
           final original = ContentBlock('Original');
@@ -730,6 +748,24 @@ void main() {
         });
       });
 
+      group('resolvedAlign', () {
+        test('defaults to centerLeft when align is not set', () {
+          final widget = WidgetBlock(name: 'Test');
+
+          expect(widget.align, isNull);
+          expect(widget.resolvedAlign, ContentAlignment.centerLeft);
+        });
+
+        test('uses explicit align when set', () {
+          final widget = WidgetBlock(
+            name: 'Test',
+            align: ContentAlignment.topRight,
+          );
+
+          expect(widget.resolvedAlign, ContentAlignment.topRight);
+        });
+      });
+
       group('copyWith', () {
         test('copies with new name', () {
           final original = WidgetBlock(name: 'Original');

packages/superdeck/lib/src/builtins/image_widget.dart

@@ -119,7 +119,7 @@ class ImageWidget extends StatelessWidget {
       styleSpec: StyleSpec(
         spec: spec.image.spec.copyWith(
           fit: _data.fit.toBoxFit,
-          alignment: alignment?.toAlignment ?? Alignment.center,
+          alignment: alignment?.toAlignment ?? Alignment.centerLeft,
         ),
       ),
     );
@@ -129,7 +129,7 @@ class ImageWidget extends StatelessWidget {
         : image;
 
     return Align(
-      alignment: alignment?.toAlignment ?? Alignment.center,
+      alignment: alignment?.toAlignment ?? Alignment.centerLeft,
       child: constrained,
     );
   }

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

@@ -62,9 +62,9 @@ class _BlockContainerState extends State<_BlockContainer> {
       child: content,
     );
 
-    // Apply alignment
+    // Apply alignment, falling back to the block's default when unset.
     content = Align(
-      alignment: widget.block.align?.toAlignment ?? Alignment.center,
+      alignment: widget.block.resolvedAlign.toAlignment,
       child: content,
     );
 

packages/superdeck/test/src/rendering/block_widget_test.dart

@@ -52,6 +52,23 @@ void main() {
         tester.expectBlockCount(9);
         expect(tester.takeException(), isNull);
       });
+
+      testWidgets('block without explicit align defaults to centerLeft', (
+        tester,
+      ) async {
+        await SlideTestHarness.pumpSlide(
+          tester,
+          Slide(
+            key: 'default-align',
+            sections: [
+              SectionBlock([ContentBlock('# No explicit align')]),
+            ],
+          ),
+        );
+
+        final align = tester.widget<Align>(find.byType(Align).first);
+        expect(align.alignment, Alignment.centerLeft);
+      });
     });
 
     group('scrollable behavior', () {