Changing widths of columns?

I am experimenting with Colorlib’s theme “Sparkling”. It is very nice. What I am wondering is if there is a way to change the width of the columns.
I am using a two column layout. The left is Content. The right in Navigation. I would like to see the content a little wider and the navigation a little narrower. Maybe by 50px or possibly even 100px. How would I do something like that?

Thank you for considering my question

Edit:
If this is a responsive theme than maybe they should not be changed.

The main reason I wanted the content area larger was to allow me to cut and paste a table from the DEA website into my blog. The table was created with larger margins than what the content area on my screen will allow. So the table extends out of the content area and is cut off by the navigation. I tried to take a snippet of the table so it could be resized but they come out too fuzzy.