fix(theme): adjust error colors in ms cupcakes theme

closes monkeytypegame#6370

Author: Miodec

frontend/static/themes/ms_cupcakes.css

@@ -5,8 +5,8 @@
   --sub-color: #d64090;
   --sub-alt-color: #edf8fa;
   --text-color: #0a282f;
-  --error-color: #000000;
-  --error-extra-color: #c9c9c9;
-  --colorful-error-color: #ca4754;
-  --colorful-error-extra-color: #7e2a33;
+  --error-color: #a4dd32;
+  --error-extra-color: #90bd34;
+  --colorful-error-color: #a4dd32;
+  --colorful-error-extra-color: #87b330;
 }