Merge branch 'add-button-styles-ux-guide' into 'master'

Document button secondary states

## What does this MR do?
Document the changes from #24145 and !7797.

It also updates the icons and color section in the basics page.

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
#24145

cc @awhildy

See merge request !7924

1 files changed, 0 insertions, 0 deletions

diff --git a/doc/development/ux_guide/img/button-success-secondary--hover.png b/doc/development/ux_guide/img/button-success-secondary--hover.png
new file mode 100644
index 00000000000..4af2a68cf1b
--- /dev/null
+++ b/doc/development/ux_guide/img/button-success-secondary--hover.png