Either you have to go into the jat3 files to do this or you should be able to just add the code to the end of your template.css. Either way note what you did because you will lose the changes on upgrade (unless you are using a theme)
For active
.ja_orisite .ja-tabs-title-top ul li.active h3, .ja_orisite .ja-tabs-title-top ul li.firstactive h3, .ja_orisite .ja-tabs-title-top ul li.lastactive h3 {
}
For others
.ja_orisite .ja-tabs-title-top ul.ja-tabs-title li h3 {
- font-size: 100% !important;
- line-height: 50px;
- color: #A5A6A7;
- font-weight: normal;
- font-style: normal;
}
and the main file is here
plugins/system/jatabs/jatabs/themes/ja_orisite/style.css
Hope that helps you