changed variable names and removed unnecesary vars

@boonrs tweaked the variable names and removed a couple of variables because they never change regardless of the color.

$primary-color > $background-color
$secondary-color > $header-color
$tertiary-color > $border-color
$text-color - stays the same
$text-color-dark - removed
$light-background-text-color - removed
$tooltip-color - removed
$dimple-fill - removed

I would argue that we should pull all colors out as variable, to save someone having to manually go through and update in the future. But will defer to your judgement.