Please, find attached a sample project of RadEditor with <p>
tags reset to zero padding and margin.
The selectors that reset the default values of these tags are at the bottom of customeditor.css file, i.e:
margin: 0px !important;
padding: 0px !important;
The CSS selectors are case-sensitive, so make sure that you keep the casing, i.e. P != p
Have a great weekend,
the Telerik team