Limit height of code blocks (#3012)

* Limit height of code blocks

Users often post lengthy code or configuration listings which makes following the actual discussion difficult. Therefore we limit a code block by half a screen while still being able to scroll through the code listing itself.

* Define a minimal code block height for small screens

* Add max-height compatibility for browsers that don't support `max()`

See https://caniuse.com/css-math-functions

* Less has a built-in `max` function, so we need to escape this value

Co-authored-by: David Wheatley <hi@davwheat.dev>

less/forum/Post.less

@@ -147,6 +147,9 @@
       border-radius: 0;
       display: block;
       overflow-x: auto;
+      // Backwards compatibility for browsers that don't support `max()`
+      max-height: 50vh;
+      max-height: ~"max(50vh, 250px)";
     }
   }
   h1, h2, h3, h4, h5, h6 {