Sideframe is a package for creating sideframes that are glued to another parent frame. This can be used to display a menu or a dashboard for example. If you want to maximize a frame that has sideframes, use the sideframe-toggle-maximized function that computes the size properly.

Usage example:

(sideframe-make 'left  32)
(sideframe-make 'right 32)
(sideframe-toggle-maximized)

If you're using a theme that has both dark and light modes, you can also assign a different mode to the side frame (here with nano theme):

(sideframe-make 'left 32 'dark `((foreground-color . ,nano-dark-foreground)
                                 (background-color . ,nano-dark-background)))