chore: make rating button violet for darkmode.

Purple is too dark for darkmode and is not clearly visible

styles.css

@@ -33,7 +33,7 @@
   --font-color-christmas_message: pink;
   --lyrics-text-color: lime;
   --yml-btn: yellow;
-  --rate-song-btn: purple;
+  --rate-song-btn: violet;
   --grey: grey;
   font-family: "Roboto", sans-serif;
 }