@@ -20,10 +20,10 @@
  * A single module. Keeps track of its own active state and settings.
  */
 
-function Spinner( { isSaving } ) {
+function Spinner( { isSaving, className } ) {
 	return (
 		<span
-			className="spinner"
+			className={ [ 'spinner', className ].join( ' ' ) }
 			style={ {
 				display: ( isSaving ? 'inline-block' : 'none' ),
 				float: 'none',
/**
 * Spinner component.
 *
 * Site Kit by Google, Copyright 2021 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * A single module. Keeps track of its own active state and settings.
 */

function Spinner( { isSaving } ) {
	return (
		<span
			className="spinner"
			style={ {
				display: ( isSaving ? 'inline-block' : 'none' ),
				float: 'none',
				marginTop: '0',
				visibility: 'visible',
			} }
		/>
	);
}

export default Spinner;

Please use the `classnames` package for dynamic class names. We already use it in many places and is our go-to utility for this kind of thing  