Basic flex support

packages/core/lib/src/core_widget_factory.dart

@@ -681,10 +681,18 @@ class WidgetFactory {
           ..[kCssDisplay] = kCssDisplayBlock
           ..tsb.enqueue(TextStyleOps.fontStyle, FontStyle.italic);
         break;
+      case 'div':
+        final displayExpressions = meta.element.styles.where((element) => element.property == 'display');
+        final displayExpression = displayExpressions.isNotEmpty ? displayExpressions.first : null;
+        final display = displayExpression?.term ?? 'block';
+        if (display == 'flex') {
+          meta.register(_flexOp(meta));
+        }
 
+        meta[kCssDisplay] = kCssDisplayBlock;
+        break;
       case 'article':
       case 'aside':
-      case 'div':
       case 'figcaption':
       case 'footer':
       case 'header':
@@ -1150,14 +1158,103 @@ class WidgetFactory {
     return baseUrl.resolveUri(uri).toString();
   }
 
+  /// Builds custom widget for div elements with display: flex from [meta]
+  BuildOp _flexOp(BuildMetadata meta) {
+    return BuildOp(
+      onChild: (childMeta) {
+        childMeta.register(_flexItemOp(childMeta));
+      },
+      onWidgets: (meta, widgets) {
+        final String id = meta.element.id;
+        String flexDirection = 'row';
+        String justifyContent = 'flex-start';
+        String alignItems = 'flex-start';
+
+        for (final element in meta.element.styles) {
+          final String? value = element.term;
+
+          if (value != null) {
+            switch (element.property) {
+              case 'flex-direction':
+                flexDirection = value;
+              break;
+              case 'justify-content':
+                justifyContent = value;
+              break;
+              case 'align-items':
+                alignItems = value;
+              break;
+            }
+          }
+        }
+
+        return [
+          Flex(
+            key: Key(id),
+            direction: 'row' == flexDirection ? Axis.horizontal : Axis.vertical,
+            mainAxisAlignment: _toMainAxisAlignment(justifyContent),
+            crossAxisAlignment: _toCrossAxisAlignment(alignItems),
+            children: widgets.toList()
+          )
+        ];
+      },      
+    );
+  }
+
+  /// Build op for child elements of flex containers
+  BuildOp _flexItemOp(BuildMetadata meta) {
+    return BuildOp(
+      defaultStyles: (element) {
+        return {
+          kCssWidth: "auto",
+          kCssHeight: "auto"
+        };
+      }
+    );
+  }
+
+  /// Converts CSS [justifyContent] to Flutter Grid MainAxisAlignment
+  static MainAxisAlignment _toMainAxisAlignment(String justifyContent) {
+    switch (justifyContent) {
+      case 'flex-start':
+        return MainAxisAlignment.start;
+      case 'flex-end':
+        return MainAxisAlignment.end;
+      case 'center':
+        return MainAxisAlignment.center;
+      case 'space-between':
+        return MainAxisAlignment.spaceBetween;
+      case 'space-around':
+        return MainAxisAlignment.spaceAround;
+      case 'space-evenly':
+        return MainAxisAlignment.spaceEvenly;
+      default:
+        return MainAxisAlignment.start;
+    }
+  }
+
+  /// Converts CSS [alignItems] to Flutter Grid CrossAxisAlignment
+  static CrossAxisAlignment _toCrossAxisAlignment(String alignItems) {
+    switch (alignItems) {
+      case 'flex-start':
+        return CrossAxisAlignment.start;
+      case 'flex-end':
+        return CrossAxisAlignment.end;
+      case 'center':
+        return CrossAxisAlignment.center;
+      case 'baseline':
+        return CrossAxisAlignment.baseline;
+      case 'stretch':
+        return CrossAxisAlignment.stretch;
+      default:
+        return CrossAxisAlignment.start;
+    }
+  }
+
   BuildOp _anchorOp(String id) {
     final anchor = GlobalKey(debugLabel: id);
 
     return BuildOp(
-      onTree: (meta, tree) {
-        _anchorRegistry.register(id, anchor);
-        tree.registerAnchor(anchor);
-      },
       onTreeFlattening: (meta, tree) {
         final widget = WidgetPlaceholder('#$id').wrapWith(
           (context, _) => SizedBox(