Merge pull request #454 from TaeMochi12/patch-1

Added one guide for learning flexbox in css.

README.md

@@ -322,6 +322,7 @@ Please see [CONTRIBUTING](https://github.com/DhanushNehru/Ultimate-Web-Developme
 - [CSS Tutorial - Zero to Hero (Complete Course)(Freecodecamp)](https://www.youtube.com/watch?v=1Rs2ND1ryYc)
 - [CSS tips and tricks - Kevin Powell](https://www.youtube.com/kepowob)
 - [Introduction to CSS - Web Dev Simplified](https://www.youtube.com/playlist?list=PLZlA0Gpn_vH9D0J0Mtp6lIiD_8046k3si)
+- [A Complete Guide to Flexbox](https://css-tricks.com/snippets/css/a-guide-to-flexbox/)
 
 ## JS Learning Resources
 - [Learn JavaScript - Full Course for Beginners (YouTube - FreeCodeCamp)](https://www.youtube.com/watch?v=PkZNo7MFNFg)