Fix undefined variable in _settings.scss

ON line 371 the $button-border-color is using a undefined variable $bg I changed it to $button-bg.
Fixes https://github.com/zurb/foundation/issues/5200 :
Child selector added to 'dd' to select only accordion CHILDREN <dd> elements.
add button support for pagination
Merge branch 'master' of https://github.com/zurb/foundation
small.error and span.error seem to be interchangeable for holding Abide error messages. Added a missing `.error span.error` selector.
Change icon-bar to use -html-icon-bar-classes variable
Fix a minor typo with one of the warnings within a mixin associated with the accordion compontent
Merge pull request #5412 from Costent/master

Add button support for pagination
Document -html-icon-bar-classes variable
Merge branch 'master' of github.com:zurb/foundation
Ensure the value of -style for the icon-bar mixin is actually accounted for with its output
Merge branch 'master' of https://github.com/zurb/foundation
Added 'Semantic Markup with CSS' section to Icon Bar Component Page
Change documentation of button mixin to be consistent with the other componeents
Merge pull request #5390 from jameswlane/patch-1

Fix undefined variable in _settings.scss
Merge pull request #5402 from cautionbug/master

Accordion 'dd' overreach on active change
Merge branch 'master' of https://github.com/zurb/foundation
Rollup master changes