Something that I think about and work on a lot is writing better CSS. Trial and error and reading have led me to adopting practices like declaring box-sizing: border-box on sites
to simplify any box-model related code I write, or setting the height and width on pages to 100vw/vh to ensure a concrete value that scales with device width. But I'm curious what the DEV community has to say about this: what are the most integral CSS properties that you add to every project?