una.im | Using color-mix() to create opacity variants
HTML Color Mixer
Mattia Astorino on Twitter: "The new #css Color Module 5 working draft will introduce new functions to manipulate colors! (previous as color-mod) 🔥 - color-adjust() - color-mix() - color-contrast() https://t.co/f1zHh2aGKN https://t.co/T3eMoCk6oy" /
Color Wheels
A Nerd's Guide to Color on the Web | CSS-Tricks - CSS-Tricks