Created by: yankee42
The color levels used in alerts: https://github.com/twbs/bootstrap/blob/c13ec3ea937c21994f5cffc1d759869af6747227/scss/_alert.scss#L49
And in tables: https://github.com/twbs/bootstrap/blob/c13ec3ea937c21994f5cffc1d759869af6747227/scss/_tables.scss#L105
Come from a variable. However the color level for list-group-item is hard coded: https://github.com/twbs/bootstrap/blob/c13ec3ea937c21994f5cffc1d759869af6747227/scss/_list-group.scss#L159
This does strike me as inconsistent. I think all these options should be equally customizable. This PR fixes this by also putting the color levels for list-group-items into a variable.
Also note, that the default value for alert&table are both -10 and 6 for background and color respectively. However the defaults for list-group-item ist -9 and 6 for background and color respectively. I did not change this (yet) as I am not sure whether this might be on purpose.