Use this document and a guide, not a literal code bible. This guide has never been updated with the subsequent PeopleTools releases, but it does provide good insight into the delivered styles available for your pages.
PeopleSoft published the “CSS Guide for PeopleSoft Fluid User Interface” in 2015 with PeopleTools 8.54. PeopleSoft Fluid User Interface Supplemental Documentation (Doc ID 1909955.1) It will provide the basics to get you started. This paper is not a definitive guide for all fluid image techniques. We assume the reader understands the basic concepts of developing a Fluid application and using images on classic pages. This paper is an introduction to applying delivered PeopleSoft styles to images on a Fluid UI Page. The delivered PeopleSoft CSS Styles can be used for both. The good news is that Fluid treats all images the same, whether they are Design Time Images or User Uploaded Images.
The only real difference is that we now use the “Fluid” tab on the Page Field Properties to control how that image displays. The tools for placing images on a page are those same tools we use on classic pages. Images are an important part of the modern User Experience (UI). Properly constructed, one page will meaningfully adjust to multiple different displays from a desktop to a mobile phone at runtime. PeopleSoft Fluid UI allows developers to create pages that adapt to the user’s screen. PeopleTools Project with all Demo Objects (zip) Download Introduction