On Bootstrap 4 Alpha 6 a variable is not there anymore

[slakbal]

Love this little component... on alpha 6 the SASS variable $font-size-root doesn't exist anymore.
Using $font-size-base should also work but in the following calculation you are doing:

CURRENT:

top:(2 * $input-padding-y + $font-size-base*$line-height-base + 2 * $input-btn-border-width/**$font-size-root**) !important;

NEW:

top:(2 * $input-padding-y + $font-size-base*$line-height-base + 2 * **$input-btn-border-width**/**$font-size-base**) !important;

This however creates an error when compiling because $input-btn-border-width is in pixels and $font-size-base is in rem. Which of-course makes the division problematic.

Unfortunately my knowledge of the px : rem ratios in bootstrap is a bit limited. Thought I'd rather ask you what a proper solution is.