Include the GraphiQL stylesheet

Signed-off-by: Dominik Henneke <dominik.henneke@sda-se.com>

.changeset/light-insects-sort.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-api-docs': patch
+---
+
+Include the GraphiQL stylesheet

plugins/api-docs/src/components/GraphQlDefinitionWidget/GraphQlDefinitionWidget.tsx

@@ -14,11 +14,12 @@
  * limitations under the License.
  */
 
-import React, { Suspense } from 'react';
-import { buildSchema } from 'graphql';
-import { makeStyles } from '@material-ui/core/styles';
 import { Progress } from '@backstage/core';
 import { BackstageTheme } from '@backstage/theme';
+import { makeStyles } from '@material-ui/core/styles';
+import 'graphiql/graphiql.css';
+import { buildSchema } from 'graphql';
+import React, { Suspense } from 'react';
 
 const GraphiQL = React.lazy(() => import('graphiql'));