Used min height to fix for small screens.

app/assets/javascripts/api.js

@@ -98,7 +98,6 @@ const Api = {
   },
 
   commitMultiple(id, data, callback) {
-    // see https://docs.gitlab.com/ce/api/commits.html#create-a-commit-with-multiple-files-and-actions
     const url = Api.buildUrl(Api.commitPath)
       .replace(':id', id);
     return $.ajax({

app/assets/stylesheets/pages/repo.scss

@@ -234,7 +234,7 @@
       vertical-align: top;
       width: 20%;
       border-right: 1px solid $white-normal;
-      min-height: calc(100vh + 20px);
+      min-height: 475px;
       height: calc(100vh + 20px);
       overflow: auto;
     }