How to hide left column on mobile devices?

On mobile devices, the left column takes up way too much space. So I'd like to do 2 things:

1- Hide the left column on mobile devices only
2- Move the display of the author name from the left column to the main/right column

I am a web developer, comfortable with PHP and CSS, though I'm not at all familiar with the punbb source code. I'm comfortable making css/js/php changes if I'm guided as to where those changes should be made. I opened the page shown in my screenshot in Chrome Developer Tools and tried to set display:none on every span I could find related to that left column, but the entire column never disappeared. I'm wanting the whole column to hide and the right column to expand to fill the entire width of the page, on mobile devices only. I also see in the inspected css that there are mobile-specific css directives. It seems the best approach would be to modify those to hide the left column (mobile only), but I can't figure out how to do it.

And how do I display author name at the top of the main content column?

Thanks in advance.