Created by: andresgalante
This PR fixes #24600 (closed) and changes colors references on variables.scss from hardcoded to variables on the theme to keep consistency.
@mdo @XhmikosR there are 2 colors that are not on our color variables but can be closely achieved with darken and lightnen functions of $red and $yellow:
https://github.com/twbs/bootstrap/blob/v4-dev/scss/_variables.scss#L285 https://github.com/twbs/bootstrap/blob/v4-dev/scss/_variables.scss#L862
do you think it's worth it? or is it better to just leave them hardcoded?