Pipeline dropdown opens underneath change stats on commit page

Summary

When you open the pipeline tests dropdown on a commit page, it opens underneath the change stats ("X changed files with Y additions and Z deletions")

Steps to reproduce

  1. Go to clash-lang/clash-compiler@e18c38cb
  2. Click on the orange (!) icon after "Pipeline #39755288 passed with stage"

What is the current bug behavior?

The dropdown list opens underneath the change stats.

What is the expected correct behavior?

The dropdown list opens above the change stats.

Relevant logs and/or screenshots

Screenshot_2018-12-12-pipeline-dropdown

Output of checks

This bug happens on GitLab.com

Possible fixes

It seems both the dropdown list and the change stats have a z-index of 200. I think the dropdown list z-index should be increased.

https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/stylesheets/pages/pipelines.scss#L981

But I have no idea if this would have any other unwanted effects.