Fix snackbar styling issue

interface/src/components/SnackbarNotification.js

@@ -7,8 +7,7 @@ import CloseIcon from '@material-ui/icons/Close';
 
 const styles = theme => ({
   close: {
-    width: theme.spacing.unit * 4,
-    height: theme.spacing.unit * 4,
+    padding: theme.spacing.unit / 2,
   },
 });