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Problem

Some various states of styling in the keyboard navigation plugin are difficult today, see: google/blockly-keyboard-experimentation#511.

Request

Many of the 'has' styling cases (and some of the other existing, unsolved problems) could benefit from having a few new CSS classes that properly represent different state situations:

• blocklyTreeHasActiveFocus for cases when a tree has a node with active focus that isn't the tree root.
• blocklyTreeHasPassiveFocus for cases when a tree has a node with passive focus that isn't the tree root.
• blocklySubtreeHasActiveFocus for cases when a tree has a subtree (such as the flyout's workspace) has a node with active focus that isn't the subtree root.
• blocklySubtreeHasPassiveFocus for cases when a tree has a subtree (such as the flyout's workspace) has a node with passive focus that isn't the subtree root.
• blocklyFieldHasEditorOpen for cases when a field is being actively edited.

Alternatives considered

Using the :has() CSS pseudo-class, however this requires a version of Safari that may introduce compatibility issues for Blockly & Blockly applications. It also may not be sufficient to solve all known styling problems that have been identified in the keyboard navigation plugin.

Additional context

No response