I don't think it is a good way to do that. It will strongly limited
the way of customize report. 

There should be a templates, which can be edit by HTML designer. It's important that the HTML designer should not have to learn a script language to do the design. They should be able open a template with their often used HTML editor. And edit it as a normal webpage, but for the data part, they can put some special label instead. And then the report generate engine should replaces several labels in the template to generated the report.

Combining generation code and HTML makes designer without programming knowledge hard to edit the template.

All style should be controlled by CSS. And no Inline Style should be used. It's better use linked style, and copy the choosen CSS file to the same location of the report.

Or, you can generate report in XML format, and use different XLST to generate different style of report.

All the above methods are designed to seperate generation and the HTML template, and seperate data and representation.