Question regarding Custom Fields and CSS Class

I try to change the size of the heading field for custom fields, but i only can change it for all fields by setting:

h3.eb-heading {
display: block;
}
In the file Style.css

I tried to define a own class for specific fields. So i wrote in the field for CSS-Class "waf1" and tried to adress it by the style.css like:

h3.waf1 {
font-size: small;
}

But this dont work. I have no further idea how to solve this and i am really happy if anybody can help me here

I should be able to help you. Could you post a link to a sample page(s) and indicate the fields that you'd like to control the stying on?