[tex4ht] How to add custom Css code into the configuration file? @media

[Nasser M. Abbasi]

I am trying to add this custom code into my .cfg file, using \Css{...}
that I always used, but it gives syntax error.


The code works fine if I add it manually to the index.css file
after compiling. But I need to put it to my .cfg file so it automatically
go inot each generated .css

The code is below. I got it from this web site

https://www.thatcompany.com/making-fixed-width-website-mobile-friendly

-------------------

@media only screen and (min-width: 100px) and (max-width: 960px) {
body{margin-top: 1em; margin-bottom: 1em;
      width: auto; max-width: 90%; margin-left: auto;
      margin-right: auto; padding: 0em; color: #444;
      font-family: arial, sans-serif; line-height: 1.5;
      font-style: normal; font-size: 1.0em;
      text-align:justify; background: #FFFFFF;}
------------------------

in the .cfg file for tex4ht, I just added \Css{..} to the above giving

-------------------
\Css{@media only screen and (min-width: 100px) and (max-width: 960px) {
body{margin-top: 1em; margin-bottom: 1em;
      width: auto; max-width: 90%; margin-left: auto;
      margin-right: auto; padding: 0em; color: #444;
      font-family: arial, sans-serif; line-height: 1.5;
      font-style: normal; font-size: 1.0em;
      text-align:justify; background: #FFFFFF;}
}
-----------------

But when I compile with make4ht, the error is

Runaway argument?
{@media only screen and (min-width: 100px) and (max-width: 960px) { b\ETC.
! Paragraph ended before \Css was complete.
<to be read again>
\par


Is the problem the use of @ in media?

Thank you,
--Nasser