Fix fit using correct dims on demo

This doesn't add the debounce suggested in the issue, but it does
comment about it.

Fixes #4114

demo/index.css

@@ -7,6 +7,7 @@ body {
     height: 100vh;
     display: grid;
     grid-template-rows: 24px 1fr;
+    overflow: hidden;
 }
 
 #banner {
@@ -41,11 +42,6 @@ body {
     color: #fff;
 }
 
-#terminal-container {
-    height: 60%;
-    margin: 0 auto;
-}
-
 p {
     font-size: 0.9em;
     font-style: italic