Option to put Images/Embeds/Tables in full width still using boxed width page

Within a limited width document I would like to allow some content types like images, embeds and tables to take up a little more of the screen. Certain types of content require a little more space to fit together better. It doesn't necessarily need to be 100%, but 60% would be perfect (maybe one day it won't allow customizing the window size).

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Image from Medium