There are two avenues of customizing the Abstract Play interface:

• Palettes let you simply change the colours assigned to each player. For most games and situations, this is enough.
• Custom CSS is also possible for situations where you want more fine-grained control over many different aspects of how the board is rendered. This is not for the faint of heart. It requires a working knowledge of CSS and the ability to inspect and read HTML in the developer console. While it is possible to just copy and paste CSS code from others, this is not without risk. You should never inject code you don't understand yourself or aren't confident came from a trusted source!