Wrap the empty workspace in paper to get the right background in dark mode

src/components/Workspace.js

@@ -3,6 +3,7 @@ import PropTypes from 'prop-types';
 import { styled } from '@mui/material/styles';
 import classNames from 'classnames';
 import Grid from '@mui/material/Grid';
+import Paper from '@mui/material/Paper';
 import Typography from '@mui/material/Typography';
 import { visuallyHidden } from '@mui/utils';
 import Window from '../containers/Window';
@@ -83,6 +84,11 @@ export class Workspace extends Component {
     const { t } = this.props;
 
     return (
+      <Paper
+        style={{
+          height: '100%',
+        }}
+      >
         <Grid
           alignItems="center"
           container
@@ -103,6 +109,7 @@ export class Workspace extends Component {
             </Typography>
           </Grid>
         </Grid>
+      </Paper>
     );
   }