Concern about website container area

I have an other concern about my website container area.
I been haven this code to make my container are look bigger:

.container {
  max-width: 90% !important;
  width: 90% !important;

It working... But, I can't put my image and text full screen so to speak. For example, I tried very big images but they re not filling the hole container area (like on this example
What I'm trying to do is to make my container area bigger so images and text can have more space.

This are the test I did:
# I made an other test without side bar, same result. The container still small (same page).

# Its looks like the CSS code is not only making the container bigger but the widget bar and the space between too (like on this image). The continuer still small

This are my questions:

2) Is it possible to modify in the CSS code to got a better result?
3) Is it possible to make the container bigger without making the side bar become bigger too?

Thank you in advance.