Utilidades CSS

Cargadores con CSS
https://cssloaders.github.io/

Formas geométricas
https://css-tricks.com/the-shapes-of-css/

Sombras:
https://cssdeck.com/labs/16-box-shadows-to-save-your-time

https://www.hongkiat.com/blog/creative-css-shadows/

Generadores CSS de background

UI:

https://uxdesign.cc/how-to-improve-your-product-ui-designers-checklist-58510947e6ab

https://www.refactoringui.com/

100 animaciones increíbles y fáciles de usar:

https://dev.to/afif/another-100-underline-overlay-animations-the-extended-css-collection-574c

https://www.webdesignerdepot.com/2014/05/8-simple-css3-transitions-that-will-wow-your-users/

https://daneden.github.io/animate.css/

https://1stwebdesigner.com/css-effects/

100.000 iconos gratis, nada menos:

https://www.iconshock.com/freeicons/