Font sizes for "normal" text in Caliper is managed through the container.css file, and this is where your custom rules should go.
Open the file: <root>Portals/<portal where you have the skin installed>/Containers/Caliper/container.css
Here you will find the main styling rules for the containers. You will notice that the styling for each container is in a section with a commented header.
You must know which container's font-size you would like to change.
For instance, if you would like to change the font-size for Container2
look for ".MegaDropDownContainer .Container_2"
you will find a block of css for this container.
(Conatiner2a and Conatiner2b also use styling from ".MegaDropDownContainer .Container_2")
The general font styling for this container is under .MegaDropDownContainer .Container_2 .Normal
However, you would want to change all matching font-sizes within that block of css,
because they are the specific font-sizes for anchor tags, div tags, paragraph tags, etc. and each of these rules will
override the general font-styling inherited from .MegaDropDownContainer .Container_2 .Normal