With modern frameworks and CSS-in-JS you don't have to worry about these anymore but still it would be a good idea to get familiarized with BEM atleast.
Build Tools
Task Runners
npm scripts
Linters and Formatters
ESLint
Prettier
CSS Preprocessors
PostCSS
Sass
1
CSS Architecture
BEM
Package Managers
yarn
npm
Web Security Knowlege
CORS
Content Security Policy
OWASP Security Risks
0
HTTPS
Version Control Systems(What are they and why you should use one