[4.0] configuration tab background (#22505)

* [4.0] configuration tab background

Small tweak to the background colour of the active color to increase the contrast between active and non-active tabs

* Revert "[4.0] configuration tab background"

This reverts commit 79c640e.

Do the work in the variaables.scss

* make the change in a variable

* oops

administrator/templates/atum/scss/_variables.scss

@@ -125,7 +125,7 @@ $dropdown-spacer:                  0;
 // Tabs
 $nav-tabs-border-width:            0;
 $nav-tabs-border-radius:           0;
-$nav-tabs-link-active-bg:          rgba($black, .1);
+$nav-tabs-link-active-bg:          rgba($black, .2);
 
 // Tables
 $table-border-width:               1px;