add note to CONTRIBUTING.md about `outline: none`

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7d7b0fb6a656c37757c394fc003b5b03204beec3..9460c8db7af5c95f471b5399e8f923cda3d7766f 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -174,6 +174,7 @@ license your work under the terms of the [MIT License](LICENSE.md).
 - Series of classes for a component should include a base class (e.g., `.component`) and use the base class as a prefix for modifier and sub-components (e.g., `.component-lg`).
 - Avoid inheritance and over nesting—use single, explicit classes whenever possible.
 - When feasible, default color palettes should comply with [WCAG color contrast guidelines](http://www.w3.org/TR/WCAG20/#visual-audio-contrast).
+- Except in rare cases, don't remove default `:focus` styles (via e.g. `outline: none;`) without providing alternative styles. See [this A11Y Project post](http://a11yproject.com/posts/never-remove-css-outlines/) for more details.
 
 ### JS