Hi Diane. The footer widgets font size is being set elsewhere by the theme using the same selectors (.footer-widgets .widget). To override that we just need to target the elements more specifically. We do that by adding another selector. Give this a try:
.footer-widgets .inside-footer-widgets .widget {
font-size: 12px;
}
You mentioned wanting to learn more about CSS. Here are three articles that explain more about CSS and how it is applied. Good references:
http://www.htmldog.com/guides/css/beginner/
http://www.w3schools.com/css/default.asp
http://www.w3.org/Style/Examples/011/firstcss.en.html