fix: youtube video size

Author: antfu

guide/why.md

@@ -66,4 +66,6 @@ $ npm init slidev
 
 Or have a quick preview of it:
 
-<iframe width="560" height="315" src="https://www.youtube.com/embed/eW7v-2ZKZOU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+<div class="aspect-9/16 relative">
+<iframe class="rounded w-full shadow-md border-none" src="https://www.youtube.com/embed/eW7v-2ZKZOU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+</div>