This was confusing for me too until I understood the parent/child hierarchy. When you apply a class to an object in forms, it applies that class to the parent element called an li.

Any css you apply directly to the class applies only to the parent element and not children elements unless specified after the class name.

To see the child elements you can use the google developer tools. Press F12, then Ctrl+Shift+C and as you mouse over the element you will see the li element but as you mouse around inside of the object you will see the types of child elements it has.

I am mousing over the table header and I can see that the child object is called an h2. So all you have to do to edit that object is define your CSS like this, following the class name with a space and the child object type.

.yourTableClassName h2 {
font-size: 20px;
}

If there are multiple child objects of the same type, all will be effected.