mouse position placement
All the custom setting about grid, ruler, guide must be backup in a project file of course !!!
I think the css tool that implement all this functionnalities don't exist, at this time only raster and vector tool support this. I think the only way for a css editor is to override browser with editor functionnalities, only developper that have access to engine code could implement this so the only Dominant monopole engine would be webkit . In a way if we stick to firefox , many source code plug in under BSD 2-Clause License can be use to add enhance already implemented functionnalities instead use them/make them accessible from the editor .
topstyle is not a wysiwyg IDE but perhaps could support create or import custom grid, guide .