fix(site): use purple for attr's color (#3406)

Author: shenjunjian

examples/sites/src/assets/custom-markdown.css

@@ -162,7 +162,7 @@ html.dark.dark .markdown-body code {
       color: #e1e4e8;
     }
     .attr-name {
-      color: #f97583;
+      color: #b392f0;
     }
     .attr-value {
       color: #9ecbff;