Problem with responsiveness with left sidebar

I’m having trouble with the NIRVANA theme responsiveness – it affects viewing on a mobile phone and on a desktop when I reduce the size of the browser window.

My layout is content with one sidebar on the LEFT. If I reduce the browser window width, everything is fine until the LEFT sidebar drops beneath the content – it’s below, but LEFT justified which means that there’s a lot of white space to the LEFT of the content.

As I reduce screen width further, the white space stays so the content width is always half the screen width. This looks bad enough on a desktop, but on a mobile it means that only a few letters of the content can be seen before it wraps to the line below.

Anyone have any ideas what is going on and how I can get this sorted?

Thanks