fix: use highlight color for mark

Author: pengx17

custom.css

@@ -571,7 +571,7 @@ mark {
   font-size: inherit;
   text-decoration-style: solid;
   text-decoration: underline;
-  text-decoration-color: var(--ct-warning-color);
+  text-decoration-color: var(--ct-highlight-color);
   text-decoration-thickness: 3px;
   text-decoration-skip-ink: none;
   text-underline-offset: -1px;