a11y: `header` => `div.jp-stack-panel-header` in all @jupyterlab/debugger panels

packages/debugger/src/panels/breakpoints/header.ts

@@ -15,7 +15,9 @@ export class BreakpointsHeader extends Widget {
    * Instantiate a new BreakpointsHeader.
    */
   constructor(translator?: ITranslator) {
-    super({ node: document.createElement('header') });
+    super({ node: document.createElement('div') });
+    this.node.classList.add('jp-stack-panel-header');
+
     translator = translator || nullTranslator;
     const trans = translator.load('jupyterlab');
 

packages/debugger/src/panels/callstack/header.ts

@@ -15,7 +15,9 @@ export class CallstackHeader extends Widget {
    * Instantiate a new CallstackHeader.
    */
   constructor(translator?: ITranslator) {
-    super({ node: document.createElement('header') });
+    super({ node: document.createElement('div') });
+    this.node.classList.add('jp-stack-panel-header');
+
     translator = translator || nullTranslator;
     const trans = translator.load('jupyterlab');
 

packages/debugger/src/panels/sources/header.tsx

@@ -21,7 +21,9 @@ export class SourcesHeader extends Widget {
    * @param model The model for the Sources.
    */
   constructor(model: IDebugger.Model.ISources, translator?: ITranslator) {
-    super({ node: document.createElement('header') });
+    super({ node: document.createElement('div') });
+    this.node.classList.add('jp-stack-panel-header');
+
     translator = translator || nullTranslator;
     const trans = translator.load('jupyterlab');
 

packages/debugger/src/panels/variables/header.ts

@@ -15,7 +15,9 @@ export class VariablesHeader extends Widget {
    * Instantiate a new VariablesHeader.
    */
   constructor(translator?: ITranslator) {
-    super({ node: document.createElement('header') });
+    super({ node: document.createElement('div') });
+    this.node.classList.add('jp-stack-panel-header');
+
     translator = translator || nullTranslator;
     const trans = translator.load('jupyterlab');