Yes it’s just css. The hard part is deciding what colours things should be. How thick to make the borders, and when to add them. What sizes and colours and font

Yes it’s just css. The hard part is deciding what colours things should be. How thick to make the borders, and when to add them. What sizes and colours and fonts for the different bits of text. How to lay it out. This sort of design fits nicely into css and html without much hackery but that doesn’t mean it’s easy to design. I suppose you could view source or inspect element.