update header to jp-stack-panel-header in toc

packages/toc/src/toc.tsx

@@ -128,7 +128,7 @@ export class TableOfContents extends Widget {
     }
     let jsx = (
       <div className="jp-TableOfContents">
-        <div className="header">{title}</div>
+        <div className="jp-stack-panel-header">{title}</div>
       </div>
     );
     if (this._current && this._current.generator) {

packages/toc/src/toc_tree.tsx

@@ -74,7 +74,7 @@ class TOCTree extends React.Component<IProperties, IState> {
     });
     return (
       <div className="jp-TableOfContents">
-        <div className="header">{this.props.title}</div>
+        <div className="jp-stack-panel-header">{this.props.title}</div>
         {Toolbar && <Toolbar />}
         <ul className="jp-TableOfContents-content">{list}</ul>
       </div>

packages/toc/style/base.css

@@ -38,7 +38,7 @@
   height: 100%;
 }
 
-.jp-TableOfContents .header {
+.jp-TableOfContents .jp-stack-panel-header {
   border-bottom: var(--jp-border-width) solid var(--jp-border-color2);
   flex: 0 0 auto;
   font-size: var(--jp-ui-font-size0);