There are lots of resources out there for aspiring developers.
W3 Schools is a great site and it’s probably where the information is the easiest to search. Whenever I just need confirmation on that forgotten value or attribute (damn what’s that shorthand command again??) I just search W3 and find it right away.
They have snippets of code you can run to see the effects right away. Pretty neat!
Created in 1998, its name is derived from the World Wide Web. W3Schools presents thousands of code examples. By using an online editor, readers can edit examples and execute the code in a sandbox.
Before you do anything else, you have to bookmark their snippet section “A Complete Guide to Flexbox”, this is so well made and explained it’s actually an embarrassment not to use it!
It divides up the attributes between the "Flex parent" and "Flex children", which makes it very intuitive to browse.
The site itself is pretty nice to dive into with a blog-style layout.
You can directly open their Snippets section for an in-depth dive into their resources!
MOZILLA DEVELOPER NETWORK (MDN)
THE bible! Pretty dry and complex at first (and that feeling continues later on) but extra complete and thorough. If it’s not there, chances are to doesn’t exist.
Mozilla Developer Network is a resource for developers, maintained by the community of developers and technical writers and hosting many documents on a wide variety of subjects
A great aspect is that it keeps referencing all the deprecated methods so you can keep up with the flow.
It’s especially useful for jQuery/JS methods that really well-documented there. And for the other languages as well. I could not survive without their Pseudo-class page.
Obviously it's a bit "Firefox inclined" (it's a page run by the Mozilla foundation so what do you expect) but it's packed with content!
You can instantly preview a page or play around! Here are some examples of projects built with Codepen: