TextPanel: Fix content overflow issue (#26612)

(cherry picked from commit ae3c285312)

public/app/plugins/panel/text/TextPanel.tsx

@@ -6,7 +6,7 @@ import { PanelProps, renderMarkdown, textUtil } from '@grafana/data';
 import config from 'app/core/config';
 // Types
 import { TextOptions } from './types';
-import { stylesFactory } from '@grafana/ui';
+import { stylesFactory, CustomScrollbar } from '@grafana/ui';
 import { css, cx } from 'emotion';
 import DangerouslySetHtmlContent from 'dangerously-set-html-content';
 
@@ -80,7 +80,11 @@ export class TextPanel extends PureComponent<Props, State> {
   render() {
     const { html } = this.state;
     const styles = getStyles();
-    return <DangerouslySetHtmlContent html={html} className={cx('markdown-html', styles.content)} />;
+    return (
+      <CustomScrollbar autoHeightMin="100%">
+        <DangerouslySetHtmlContent html={html} className={cx('markdown-html', styles.content)} />;
+      </CustomScrollbar>
+    );
   }
 }