If I run htlatex on
\documentclass[12pt]{article}
\begin{document}
Bla bla bla bla
\begin{center} x \end{center} \end{document}
with the setting in this question I get the code below, but my browser (mozilla firefox) does not properly center "x". How can I redefine the way that center is handled to just use some simple html tag (which my browser does understand correctly)?
<?xml version="1.0" encoding="iso-8859-1" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!--http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd-->
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<meta name="generator" content="TeX4ht (http://www.cse.ohio-state.edu/~gurari/TeX4ht/)" />
<meta name="originator" content="TeX4ht (http://www.cse.ohio-state.edu/~gurari/TeX4ht/)" />
<!-- -css,NoFonts,html,xhtml -->
<meta name="src" content="a.tex" />
<meta name="date" content="2016-10-16 19:12:00" />
</head>
<body >
<p>Bla bla bla bla </p>
<div class="center" >
<p> </p>
<p>x</p> </div>
</body>
</html>

.centerclass to centre the text. Or use the default setting and let tex4ht generate the css. – David Carlisle Oct 16 '16 at 23:27