Hi! The simple answer is that I used CSS, which you have to unlock by asking specific permission from the admin. See here: https://itch.io/docs/creators/css-guide
The more detailed, actual answer, and the one that is less appealing, is that it took several weeks and ten years of professional experience writing CSS and HTML.
You'll definitely want to apply to the admin to get the CSS unlocked for your page first.
After that, you could either take a look at w3schools to pick up the CSS skills - or my design/coding skills are available to hire if you want to email me to discuss what you need via my contact form here: http://polyducks.co.uk/contact/
