You must be use inter font for my UI. And remove realtime, code execution, user enter code then instaly show preview don't need. User enter code after click on run code buttons after show previous. Make increase height of nav, because soon i will add ads on nav. Make flex nav left side show logo text, center show ads, and Right side show run button. I hope currently add dummy ad with border dashed, with radius in ad show in center of text called advertisement. I need complete response site. When i open site in mobile I don't show preview box.