Update devtools-postmessage-perf-timeline/index.html

devtools-postmessage-perf-timeline/index.html

@@ -21,7 +21,7 @@
         and how long the message was queued before the <code>postMessage</code> handler started.
     </p>
         Used by <a href="https://learn.microsoft.com/microsoft-edge/devtools-guide-chromium/evaluate-performance/reference#view-messages-between-windows-iframes-and-dedicated-workers">View messages between windows, iframes, and dedicated workers</a>
-        in _Performance features reference_.
+        in <em>Performance features reference</em>.
     </p>
     <b>Main frame:</b>
     <button style="display: block; margin-top: 1.5em ;">Send message to iframe</button>