cool site and idea, here's 3 site UI suggestions

there's a bug when entering text into the regex area which creates new padded elements show up which makes text on the page shift, e.g. https://i.imgur.com/AFBccIn.gif

the line height in the subtitle area could be increased so the text isn't so cramped ( https://i.imgur.com/HReADcS.png )

the background color of the entire page should be darker (or use some other solution) to make the <code> looking text more distinct as code text. ( dark grey on dark blue doesn't really stand out https://i.imgur.com/8Nt9YNl.png )