Are -moz and -webkit still used? What is -webkit for?

The -webkit prefix applies to older Safari/Chromium based browsers in the same way -moz is used by Firefox.

If you need to support older versions of Firefox, Safari and Chromium (Chrome, Opera, Vivaldi, Brave and others) based browsers then it's worth considering if you need those styles applied.

Those particular browsers have a high update rate so use of older versions can be all but non-existent, check your logs/analytics to see what usage they have and make a decision based on that.

Depending on your build tools this is something you don't need to worry about. I use Webpack to compile any CSS and it uses https://github.com/postcss/autoprefixer behind the scenes to automatically add vendor prefixes in.

It uses a Browserlist file that checks the minimum browser support you have specified and bases that on what prefixes to include. Over time you can reduce your CSS bundle by removing older browser support and eliminating further prefixes, you can even do this automatically based on your own site stats, or using caniuse.com data with a country code.