Yoko Theme how to avoid changing layout on page resize.

I am using Yoko theme and I would like to know how to avoid changing the layout when the page is resized.

This is the link to my website, when the window changes to a smaller size, everything turns white. I would like to keep the same colors and layout (3cols)

If someone could share their advice about where to modify this, that would be great.

Thank you very much.