* Tweak callout for icon link
- no need to talk about `alt` for `<img>` since these don't use `<img>`
- make start of sentence more readable
* Tweak language of dropdown warning callout
* Tweak popover warning callout
* Tweak rtl warning callouts
* Tweak color warning callout
* Add/move accessibility callout for color to relevant pages
* Update site/content/docs/5.3/helpers/icon-link.md
* Update site/layouts/partials/callouts/warning-color-assistive-technologies.md
Co-authored-by: Mark Otto <markd.otto@gmail.com>
* Docs: add overflow and text color info to progress bar page
* Add example/reference for color & background helper use
* Add mention of color modes/dark mode
* Tweak link text
* Docs: add explanation of the base `.btn` class
and a callout reminding authors to at least define some focus styling if they intend to use it "naked"
* Turn callout into a warning
* Add initial heading
* Tweak callout wording
* Add .nav-underline modifier class
* Tweak sizing and spacing, add underline on hover
* Rebuild with Sass and CSS variables
* Document CSS vars
* Bump bundlewatch
