move sass invert into Util

src/styles/Util.scss

@@ -1,3 +1,8 @@
+// SASS overwrites the CSS invert function so we overwrite it back
+@function invert($v) {
+    @return #{"invert("}$v#{")"};
+}
+
 // returns $n and adds $offset when the theme is light
 @function lightOffset($n, $offset) {
     @return calc($n + $offset * var(--is_light));

src/styles/main.scss

@@ -1,8 +1,3 @@
-// SASS overwrites the CSS invert function so we overwrite it back
-@function invert($v) {
-    @return #{"invert("}$v#{")"};
-}
-
 @import "Util";
 @import "Colors";
 @import "Fonts";