Enable input focus state customization

- Add new mixin to generate and customize focus state as needed
- Adds variable to set default color
- Include clear disclaimer about customizing this—it's about users', so
don't go making everything bright red and expect them not to be
confused or alarmed.

Relevant issues: #2742, #4185, #7942, #8171, #8610, #9044

1 files changed, 1 insertions, 0 deletions

diff --git a/less/variables.less b/less/variables.less
index a500097c9..b8c7cf6c8 100644
--- a/less/variables.less
+++ b/less/variables.less
@@ -131,6 +131,7 @@
 
 @input-border:                   #ccc;
 @input-border-radius:            @border-radius-base;
+@input-border-focus:             #66afe9;
 
 @input-color-placeholder:        @gray-light;