Can't Add Icons to Header Menu

Hello!

First time using Divi - I am trying to add icons to my navigation items and they will not show up. I have set each item as a class in the menu and tried different ways to add them. For example, I have a phone number with a class of top-phone and this css which I found in a tutorial:

.top-phone {
width: 148!important;
}

.top-phone {
color: #136579!important;
font-size: 14!important;
}

.top-phone {
font-family: 'Lato';
content: "\e090";
font-size: 14px;
float: left;
}

It seems like I can't make any changes with css to individual items in the nav this way. Is there some setting in Divi that I'm missing?

I appreciate any help!