[docs-infra] Fix Display of Long Demo Code Blocks (#4046)

Author: dav-is

docs/src/components/Demo/Demo.css

@@ -228,16 +228,21 @@
   .DemoSourceBrowser {
     @apply text-xs;
     cursor: text;
+    display: flex;
 
-    & code {
+    & pre {
       /* Different fonts may introduce vertical align issues */
       display: flex;
       /* Make sure selection highlight spans full container width in Safari */
       flex-grow: 1;
+    }
+
+    & code {
       padding: 0.5rem 0;
     }
 
     & code .frame {
+      display: block;
       padding-left: 0.75rem;
       padding-right: 0.75rem;
     }