feat: improve button style and functionality

layouts/index.html

@@ -3,7 +3,9 @@
 {{ define "main" }}
     {{ $latest := index (where .Site.RegularPages "Section" "versions").ByDate.Reverse 0 }}
     <div class="coc-box" data-raw-content="{{ $latest.RawContent }}">
-        <button class="copy-btn" onclick="copyCoC()">[copy]</button>
+        <button class="copy-btn" onclick="copyCoC()" title="Copy to clipboard">
+            <img src="/markdown-icon.svg" alt="Copy" class="copy-icon">
+        </button>
         {{ $latest.Content }}
     </div>
     <p class="version-link"><a href="/versions/">Previous versions</a></p>