Allow user to customise width of reading column

On a laptop screen, the percentage of space that is used in the side bars is higher than the space used for the actual text.
Would it be possible to collapse that bar to the right on a laptop screen, and reduce the margin to the left in order to free up more space? I find reading the field guide on my laptop quite a bit more difficult than reading it on my desktop because of this.
The line length is intentional, as we are trying to optimize the line for readability by the human eye. I did some research on this at the end of last year (some good articles are here and here) and the conclusion was:
The optimal line length for your body text is considered to be 50-60 characters per line, including spaces (“Typographie”, E. Ruder).
I'm implementing a system (which uses features from the MaterializeCSS framework) which tries to keep the number of characters close to this number on various screen sizes. The example you listed above has 88 characters on the first line, and on my work desktop I have 137 characters on the first line of the same chapter, so these lines will need to become smaller.
I could try and implement a system for larger screens where the sidebars are collapsible, but this would be a idea to implement at a later date.
Perhaps it could be an option for the user to set. As I think some people prefer wider text (e.g. me). I find narrow text quite irritating and frustrating to read.
I see that it is wider if you shrink the window down a bit. I actually find that way way way easier to read.
I think we need to look at more data/ studies before concluding that 60 characters is ideal. Because I don't think that is right for everybody..
Thanks Heidi, we will implement customisable reading widths in the new Django system which is currently in development (most likely released in early 2018). User's will be able to set if they want wide, standard, or narrow reading widths, and the system will remember their preference!
Moving this to a different milestone focused on accessibility features.