fix: styles (#2729)

Author: Chasen-Zhang

src/css/markdown.scss

@@ -222,6 +222,9 @@
     &:hover {
       background-color: var(--bg-hover-copy);
       opacity: 1;
+      svg {
+        color: #fff;
+      }
     }
   }
   .theme-code-block:hover {
@@ -284,10 +287,3 @@
 .ant-image-error {
   display: none;
 }
-button.clean-btn {
-  &:hover {
-    svg {
-      color: #fff;
-    }
-  }
-}