Here are some websites to get inspiration for design and UI.
You can use them in your next project for Design Inspiration ->

1. BEHANCE
2. DRIBBLE
3. DRIBBLE
4. SCREENLANE
5. LAPA NINJA UI
6. WEBFRAME OR COLLECT-UI OR CALLTOIDEA
7. MEDIA QUERIES
8. SEARCH-MUZ-LI
9. UI-GARAGE

BONUS

1. Practice frontend on real-life projects
2. Practice CSS and get reference of syntax

Comment down your fav one