Changing sidebar widths

How can I change the widths of the sidebars in the Ari theme in my blog https://www.needleandspindle.com. I would like the right sidebar to measure 240px and the left 150px? I am trying to fit in some social media widgets in the right sidebar that are being sliced off. It doesn’t seem to be a clear case of just substituting these numbers in the code as only the left sidebar contains a width, the content column and right side bar use a percentage to determine their width.