Hi, the buttons are actually just radio-type <input> elements. I don’t think you can insert it in project pages directly, since input/form elements will be sanitized.
The project is open source. Here’s the snippet of the codes that makes the buttons if you’re interested:
Script:
https://github.com/nndda/Pitch/blob/80ac0c31949f5ef281493bcbb7d416ca868be869/src/app/scripts/themes.ts#L61C1-L74C7
Styling:
https://github.com/nndda/Pitch/blob/80ac0c31949f5ef281493bcbb7d416ca868be869/src/app/styles/_input.scss#L107C1-L140C2