Focus ring on timeline event form does not line up with input

Summary

When focused, the focus ring on the timeline event form doesn't line up exactly in the corners.

Noted in !146925 (comment 1821664578)

Steps to reproduce

1. Open an incident
2. Navigate to the Timeline tab
3. Click "Add new timeline event"
4. Focus the Timeline text editor

Example Project

gitlab

What is the current bug behavior?

Focus ring doesn't line up with border

What is the expected correct behavior?

Focus ring lines up with border

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes