Offsetting linear-gradient start point

Hi all, I’ve taken the plunge and have started to go at it alone and build my first website from scratch and I have already hit a stumbling block.

I have a fixed sidebar which sits at 160px and i want to add a linear gradient to the background of the main body.
How can I manage to get the background gradient to either begin at 160px or how to offset the gradients transition to start after 160px?

any help would be greatly appreciated

I’ve figured it out haha.