hide overflow content for single left pane (#54882)

public/app/core/components/SplitPaneWrapper/SplitPaneWrapper.tsx

@@ -94,7 +94,7 @@ export class SplitPaneWrapper extends PureComponent<Props> {
       );
     }
 
-    return leftPaneComponents;
+    return <div className={styles.singleLeftPane}>{leftPaneComponents}</div>;
   }
 
   render() {
@@ -163,6 +163,12 @@ const getStyles = stylesFactory((theme: GrafanaTheme) => {
   `;
 
   return {
+    singleLeftPane: css`
+      height: 100%;
+      position: absolute;
+      overflow: hidden;
+      width: 100%;
+    `,
     resizerV: cx(
       resizer,
       css`