Compliance fixes for gtk-3.20, gtk-4.0, and gnome-shell

This commit fixes all immediate errors that would cause `dart-sass` to error out.

Author: ran-dall

gnome-shell/_drawing.scss

@@ -79,7 +79,7 @@
 // $tc is the text color
 // $bg is the background color
 //
-  $_lbg: lightness($bg)/100%;
+  $_lbg: calc(lightness($bg) / 100%);
   @if lightness($tc)<50% { @return transparentize(white,1-$_lbg/($_lbg*1.3)); }
   @else { @return transparentize(black,$_lbg*0.8); }
 }