5.15 how to insert HTML code inside the body of a latex document?

Here is an example to insert only ONE HTML line

 
\documentclass{article}% 
\input{commonlatex} 
 
\begin{document} 
 
\ifdefined\HCode 
 \Css{body{width:70\%;}}   %this will be inserted in the HTML, only when using htlatex 
\fi 
 
\end{document}
 

To insert large amount of HTML code, use Radhakrishnan CV method:

 
\documentclass{article} 
\begin{document} 
 
\ScriptEnv{html} 
 {\NoFonts\hfill\break} 
 {\EndNoFonts} 
 
\begin{html} 
<h2>This is HTML head 2 </h2> 
 
more HTML code 
\end{html} 
 
\end{document}
 

reference: http://tug.org/pipermail/tex4ht/2013q3/000823.html