Margins for content area when in mobile narrow format

sometimes i get SO frustrated looking for all the non-standard ways to apply CSS... ARG !

Here:
townoflimon.com/index.php/alternate01

I am trying to set up an easy way for htis client to post word processing documents as HTML, to avoid the PDF problems.

As you can see, it's not too bad in full screen mode.
BUT when it is squezed down to narrow, for smart phones, there is no margin at all, that that is not good.
HOW can I apply custom CSS to this to get a margin, let's say 10 pixels, to the left and right sides of this content when narrow ?

Thanks ,
Kent

Hello,

I see you tried by adding this to /media/templates/site/museum/css/custom.css:

This is not valid. Instead, try adding this:

It will be applied only if the screen width is 414px or less (you can change this in the CSS code).

If you are testing with a mobile device, make sure you delete the mobile browser's cache after making changes to the CSS files.

Regards,
Milos