fix(editor): hide collpased content during dragging note (#10133)

Close [BS-2531](https://linear.app/affine-design/issue/BS-2531/%E6%8B%96%E5%8A%A8%E6%8A%98%E5%8F%A0%E7%9A%84note%E6%97%B6%EF%BC%8C%E4%B8%8D%E6%98%BE%E7%A4%BA%E9%9A%90%E8%97%8F%E5%86%85%E5%AE%B9), [BS-2536](https://linear.app/affine-design/issue/BS-2536/page-block%E9%A1%B6%E9%83%A8toolbar)

packages/frontend/core/src/components/blocksuite/block-suite-editor/specs/custom/widgets/edgeless-note-header.css.ts

@@ -28,6 +28,7 @@ const buttonPadding = 4;
 export const button = style({
   padding: buttonPadding,
   pointerEvents: 'auto',
+  color: cssVarV2('icon/transparentBlack'),
 });
 
 export const headerHeight = 2 * headerPadding + iconSize + 2 * buttonPadding;