It is using Ace as the code editor: <a href="https:&#x2F;&#x2F;glot.io&#x2F;about" rel="nofollow">https:&#x2F;&#x2F;glot.io&#x2F;about</a><p>&gt; Ace is used as the code editor. Make sure to check out the leftmost and rightmost tabs, where you can select language version, set a custom run command and change the editor keybindings.