fix(css-templates): add missing height to CSS editor in CssTemplateModal (#39221)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

superset-frontend/src/features/cssTemplates/CssTemplateModal.tsx

@@ -268,6 +268,7 @@ const CssTemplateModal: FunctionComponent<CssTemplateModalProps> = ({
           onChange={onCssChange}
           value={currentCssTemplate?.css ?? ''}
           language="css"
+          height="250px"
           width="100%"
         />
       </TemplateContainer>