refactor: update $css-var-prefix name

Author: lucaslarroche

scss/colors/utilities/_settings.scss

@@ -1,19 +1,9 @@
 @use "sass:map";
 @use "../../settings" as pico-settings;
 
-// String replace function
-@function str-replace($string, $search, $replace: "") {
-  $index: str-index($string, $search);
-  @if $index {
-    @return str-slice($string, 1, $index - 1) + $replace +
-      str-replace(str-slice($string, $index + str-length($search)), $search, $replace);
-  }
-  @return $string;
-}
-
 // Prefix for CSS variables
-$css-var-prefix: pico-settings.$css-var-prefix !default;
-$css-class-prefix: str-replace(pico-settings.$css-var-prefix, "--", "") !default;
+$css-var-prefix: "--pico-" !default; // Must start with "--"
+$css-class-prefix: "pico-" !default;
 
 // Palette
 $palette: () !default;