Pedigree.css is one of the external CSS stylesheets created by Tidy Legacy HTML. It contains the basic styles that are used to render the pedigree style web pages generated by Legacy and modified by Tidy Legacy HTML. By moving these styles out of the Legacy generated HTML documents and into a single external stylesheet, _LTools_ has made it easy for you to change the look and feel of your entire website. All you need to do is edit a single file.
The first time Tidy Legacy HTML is run, it creates a default external CSS stylesheet named pedigree.css in the Destination HTML Folder. Because you may have customized pedigree.css to suit your own tastes, _LTools_ will not overwrite this file the next time you run Tidy Legacy HTML. Instead it will create newpedigree.css in the Destination HTML Folder (just in case you need to refer to the original CSS settings). newpedigree.css may also contain other changes to the default CSS styles. You should compare newpedigree.css with your original/customized copy of pedigree.css to see if anything important has changed or been added since the last time you ran Tidy Legacy HTML ... especially if you have installed a more recent version of _LTools_.
If for any reason you need to restore pedigree.css to its default state, simply delete the copy of pedigree.css in your Destination HTML Folder and rerun Tidy Legacy HTML.
You can get more information on CSS and how to use it from http://www.w3schools.com/css/default.asp.
Help is also available from the Web Users Legacy (WUL) User Group.