Merge branch 'v4-dev' into v4-split-buttons

diff --cc scss/_button-group.scss
Simple merge

diff --cc scss/_dropdown.scss
Simple merge

diff --cc scss/_variables.scss
Simple merge

diff --cc scss/bootstrap.scss
index febbc4ea4a4b88975e8e3b843d0f4abde7fa1392,ef30c6b639437eb5b66be46ec9dbfbb90dd6568f..03aef0c6a4b14b803fd3f43c48113a66d6c07d4a
--- 1/scss/bootstrap.scss
--- 2/scss/bootstrap.scss
+++ b/scss/bootstrap.scss
@@@ -5,7 -5,7 +5,8 @@@
   */
  
  // Core variables and mixins
 +@import "functions";
+ @import "custom";
  @import "variables";
  @import "mixins";