Official WordPress developer resources including a code reference, handbooks (for APIs, plugin and theme development, block editor), and more.
W3C's easy-to-use markup validation service, based on SGML and XML parsers.
https://www.smashingmagazine.com/
CSS GALLERY 灵感
http://www.16sucai.com/
The world’s most popular and easiest to use icon set just got an upgrade. More icons. More styles. More Options.