Accessibility features and techniques.
My 2021 Pick: Amelia Wattenberger
Amelia is creating some of the most amazing interactive blog posts about CSS and JS. Check out this post about how percentages work in CSS!
My 2021 Pick: Miriam Suzanne
Miriam is an artist and an activist who creates software and art that celebrate the queer complexity of human experience. She's a CSS expert, and is doing an amazing job on the specifications for CSS Container Queries.