[EuiPanel] Add missing Emotion styles when panel render as button

src/components/panel/__snapshots__/panel.test.tsx.snap

@@ -1,5 +1,13 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[` 1`] = `
+<button
+  aria-label="aria-label"
+  class="euiPanel euiPanel--plain euiPanel--paddingMedium testClass1 testClass2 emotion-euiPanel-grow-m-m-plain-hasShadow-isClickable"
+  data-test-subj="test subject string"
+/>
+`;
+
 exports[`EuiPanel is rendered 1`] = `
 <div
   aria-label="aria-label"

src/components/panel/panel.test.tsx

@@ -81,5 +81,13 @@ describe('EuiPanel', () => {
         });
       });
     });
+
+    describe('onClick', () => {
+      const component = render(
+        <EuiPanel {...requiredProps} onClick={jest.fn()} />
+      );
+
+      expect(component).toMatchSnapshot();
+    });
   });
 });

src/components/panel/panel.tsx

@@ -140,6 +140,7 @@ export const EuiPanel: FunctionComponent<EuiPanelProps> = ({
       <button
         ref={panelRef as Ref<HTMLButtonElement>}
         className={classes}
+        css={cssStyles}
         {...(rest as ButtonHTMLAttributes<HTMLButtonElement>)}
       >
         {children}

upcoming_changelogs/6010.md

@@ -0,0 +1,3 @@
+**Bug fixes**
+
+Fixed issue with `EuiPanel` where the `Emotion` styles were not being passed when it was rendered as a button