format scss files below,  via csscomb

- _button.scss
- _dropdowns.scss
- docs.scss
format scss files below , by using SassBeautify

- scss/_buttons.scss
- scss/_dropdowns.scss
- scss/docs.scss

SassBeautify is plugin for sublime text
https://sublime.wbond.net/packages/SassBeautify
add new sass variable

also format '_variable.scss' by using SassBeautify
apply sass variable '$dropdown-border-radius' in some property
'$dropdown-border-radius' is used in '_dropdown.scss'