How to add css correctly

Hi, I am anxious to use your great plugin. I added some css on the page (in your plugin box) and it didn’t do anything.
No doubt this is user error, so could you please tell me what I have entered incorrectly?
Are their guidelines to entering certain code in a special way? (sorry… I’m a newbie and don’t know css so maybe I cannot use your plugin…) :o(
Also, after entering in css box, the button says schedule instead of update. Is that normal?

What I’m trying to do is to get an extra bit of line spacing between the lists

• in a

.
This is what I entered in your css box:
#contentleft ul li {
list-style-type: square;
margin: 0px 0px 20px 20px;
padding: 0px 0px 5px 0px;
line-height: 30px;
font-size: 12px;
font-family: Didactic Gothic, Trebuchet MS, Arial, sans-serif;
}
Do you think this is correct?
Do I need to add anything else to the html text box to make this work?
Thank you so much!
-kerry

https://wordpress.org/plugins/custom-css-by-techsperia/