Where can i write html5 and css3 codes?

Answer 1

if you want to do it on a computer you can use any text editor but I recommend notepad++

Answer 2

i would use c9 in the future in my own opinion, but i've heard many good things about bracket. notepad++ is one of the most recommended code editors in general as well.
https://www.quora.com/Which-is-the-best-program-to-use-for-write-HTML+CSS-code

Answer 3

In the code playground