Don't let the clipboard textarea grow too high

There are scrollbars inside the textarea in case there's a lot of text
in there. We can limit the height of the element, it looks better.

app/styles/base.css

@@ -575,6 +575,8 @@ html {
 
   box-sizing: border-box;
   max-width: 100%;
+  /* minus approximate height of title, height of subtitle, and margin */
+  max-height: calc(100vh - 10em - 25px);
 }
 
 /* Settings */