Remove the usage of Align

super_editor/lib/src/infrastructure/super_textfield/desktop/desktop_textfield.dart

@@ -1149,35 +1149,19 @@ class SuperTextFieldScrollviewState extends State<SuperTextFieldScrollview> with
 
   @override
   Widget build(BuildContext context) {
-    return _buildAlign(
-      SizedBox(
-        height: widget.viewportHeight,
-        child: SingleChildScrollView(
-          controller: widget.scrollController,
-          physics: const NeverScrollableScrollPhysics(),
-          scrollDirection: widget.isMultiline ? Axis.vertical : Axis.horizontal,
-          child: Padding(
-            padding: widget.padding,
-            child: widget.child,
-          ),
+    return SizedBox(
+      height: widget.viewportHeight,
+      child: SingleChildScrollView(
+        controller: widget.scrollController,
+        physics: const NeverScrollableScrollPhysics(),
+        scrollDirection: widget.isMultiline ? Axis.vertical : Axis.horizontal,
+        child: Padding(
+          padding: widget.padding,
+          child: widget.child,
         ),
       ),
     );
   }
-
-  Widget _buildAlign(Widget child) {
-    // Multiline textfields are already aligned correctly
-    // because they have a maxWidth constraint.
-    if (widget.isMultiline) {
-      return child;
-    }
-    // Singleline textfields have an infinity maxWidth
-    // so we need to align the whole scrollview
-    return Align(
-      alignment: _getAlignment(),
-      child: child,
-    );
-  }
 }
 
 typedef RightClickListener = void Function(

super_editor/lib/src/infrastructure/super_textfield/infrastructure/fill_width_if_constrained.dart

@@ -14,33 +14,61 @@ class FillWidthIfConstrained extends SingleChildRenderObjectWidget {
 
   @override
   RenderObject createRenderObject(BuildContext context) {
-    return _RenderFillWidthIfConstrained();
+    return RenderFillWidthIfConstrained(
+      viewportWidth: _getViewportWidth(context),
+    );
   }
 
   @override
-  void updateRenderObject(BuildContext context, RenderObject renderObject) {
-    renderObject.markNeedsLayout();
+  void updateRenderObject(BuildContext context, RenderFillWidthIfConstrained renderObject) {
+    renderObject.viewportWidth = _getViewportWidth(context);
+  }
+
+  double? _getViewportWidth(BuildContext context) {
+    final scrollable = Scrollable.of(context);
+    if (scrollable == null) {
+      return null;
+    }
+    return (scrollable.context.findRenderObject() as RenderBox?)?.size.width;
   }
 }
 
-class _RenderFillWidthIfConstrained extends RenderProxyBox {
+class RenderFillWidthIfConstrained extends RenderProxyBox {
+  RenderFillWidthIfConstrained({
+    double? viewportWidth,
+  }) : _viewportWidth = viewportWidth;
+
+  set viewportWidth(double? value) {
+    _viewportWidth = value;
+    markNeedsLayout();
+  }
+
+  double? _viewportWidth = 0;
+
   @override
   void performLayout() {
     BoxConstraints childConstraints = constraints;
 
-    // If the available width is bounded and the child did not
-    // take all available width, force the child to be as wide
-    // as the available width.
+    // If the available width is bounded, 
+    // force the child to be as wide as the available width.
     if (constraints.hasBoundedWidth) {
       childConstraints = BoxConstraints(
         minWidth: constraints.maxWidth,
         minHeight: constraints.minHeight,
         maxWidth: constraints.maxWidth,
         maxHeight: constraints.maxHeight,
       );
+    } else if (_viewportWidth != null) {
+      // If a viewport width is given, force the child to be at least this width.
+      // This is the case when this widget is placed inside an Scrollable.
+      childConstraints = BoxConstraints(
+        minWidth: _viewportWidth!,
+        minHeight: constraints.minHeight,
+        maxHeight: constraints.maxHeight,
+      );
     }
 
     child!.layout(childConstraints, parentUsesSize: true);
     size = child!.size;
-  }  
+  }
 }

super_editor/test/super_textfield/super_textfield_text_alignment_test.dart

@@ -220,8 +220,8 @@ Widget _buildSuperTextField({
     text: AttributedText(text: text),
   );
 
-  return ConstrainedBox(
-    constraints: const BoxConstraints(minWidth: 300),
+  return SizedBox(
+    width: double.infinity,
     child: SuperTextField(
       configuration: configuration,
       textController: controller,