change paragarph leading on CSS Theme

We hire a developer to customize a WordPress theme for our company website, this was some time ago and he is not available. We would like to modify the leading (space between lines in a paragraph). I went to the appearance/editor/stylesheet and downloaded a file called “style.css”that looked like this:
#ert4C p {
font-size: 9pt;
color: #000000;
margin: 0 20pt 10pt;
}
Then I added the line-height:
#ert4C p {
font-size: 9pt;
color: #000000;
margin: 0 20pt 10pt;
line-height: 130%;
}
I upload the file but nothing happens, please help me figure this out, I’m not a coder, at all!

Thank you.