CSS snippet to add space after paragraphs and headers

Could someone please show me what to put in a CSS snippet to add space after headers and paragraphs? I just want some space between them, instead of putting a blank line after each header and paragraph.

I don’t know very much about css, but I think I want to use something like margin-bottom: 10px; but I don’t know how to put this in a CSS snippet.

Thanks for your help!