Here is the some useful website that you can use.

1. Box Shadow CSS .
URL: https://getcssscan.com/css-box-shadow-examples

2. Button Hover Effects. Bellow site have many button hover effects, you can extract it’s CSS by Inspect tool.
URL: https://ianlunn.github.io/Hover/

3. Shape Divider. Useful for designing sections.
URL: https://www.shapedivider.app/

4. Animations, Apply animations on sections or any content by using this JS libraries
URL: https://animate.style/

5. Animate On Scroll Library (AOS)
URL: https://michalsnik.github.io/aos/

6. Generate CSS Filter property of any color, useful for change image color.
URL: 1] https://codepen.io/sosuke/pen/Pjoqqp
         2] https://angel-rs.github.io/css-color-filter-generator/

7. linear-gradient CSS generator
URL: 1] https://cssgradient.io/
         2] https://www.css-gradient.com