Fixed positioning of milestone dropdown in create board dropdown

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/32837

app/assets/javascripts/boards/components/board_new_form.js

@@ -72,8 +72,6 @@ import extraMilestones from '../mixins/extra_milestones';
             const milestoneDropdown = this.$refs.milestoneDropdown;
             const rect = e.target.getBoundingClientRect();
 
-            milestoneDropdown.style.left = `${rect.left}px`;
-            milestoneDropdown.style.top = `${rect.bottom}px`;
             milestoneDropdown.style.width = `${rect.width}px`;
           });
         }

app/assets/stylesheets/pages/boards.scss

@@ -669,6 +669,9 @@
 
   .dropdown-menu {
     position: fixed;
+    left: 10px;
+    top: 175px;
+    min-width: 200px;
   }
 }