Why start with an existing style guide?
When I joined DemandStar, I inherited a detailed but incomplete styleguide, and a platform that was built quickly and without a lot of attention to UI consistency. My responsibility as the sole designer at the company is to ensure that platform is usable, accessible, and as frictionless as possible. A big part of that, which is often overlooked, is visual consistency. I'm using the inherited guide as a starting point to build a styleguide full of Figma components that I can use to rapidly prototype, and that my engineering team can use as a canonical visual reference.