Fix broken colors in some themed SVGs in web UI (#34988)

app/javascript/styles/mastodon/_functions.scss

@@ -1,4 +1,6 @@
 @use 'sass:color';
+@use 'sass:string';
+@use 'sass:meta';
 
 $darken-multiplier: -1 !default;
 $lighten-multiplier: 1 !default;
@@ -19,3 +21,11 @@ $lighten-multiplier: 1 !default;
     $space: hsl
   );
 }
+
+@function hex-color($color) {
+  @if meta.type-of($color) == 'color' {
+    $color: string.slice(color.ie-hex-str($color), 4);
+  }
+
+  @return '%23' + string.unquote($color);
+}

app/javascript/styles/mastodon/basics.scss

@@ -1,14 +1,6 @@
 @use 'variables' as *;
 @use 'functions' as *;
 
-@function hex-color($color) {
-  @if type-of($color) == 'color' {
-    $color: str-slice(ie-hex-str($color), 4);
-  }
-
-  @return '%23' + unquote($color);
-}
-
 body {
   font-family: $font-sans-serif, sans-serif;
   background: var(--background-color);