feat(Alert): Transparent border bottom

mentioned in commit 05e18381

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!343 (merged)

mentioned in merge request status-page!903

mentioned in merge request gitlab-org/editor-extensions/gitlab-jetbrains-plugin!911 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4039 (merged)

mentioned in merge request gitlab!165456 (closed)

mentioned in merge request gitlab!165458 (merged)

mentioned in commit 1b0877a7

mentioned in merge request gitlab!165726 (merged)

mentioned in merge request gitlab!166177 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!50 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!51 (merged)