Fix scrollbar being hidden by header on site (#5342)

Author: rohankokane

site/src/routes/_layout.svelte

@@ -62,7 +62,6 @@
 
 <style>
 	main {
-		height: 100%;
 		position: relative;
 		margin: 0 auto;
 		/* padding: var(--nav-h) var(--side-nav) 0 var(--side-nav); */

site/src/routes/repl/[id]/index.svelte

@@ -117,7 +117,7 @@
 <style>
 	.repl-outer {
 		position: relative;
-		height: 100%;
+		height: calc(100vh - var(--nav-h));
 		--app-controls-h: 5.6rem;
 		--pane-controls-h: 4.2rem;
 		overflow: hidden;