I have Emacs 24 running in Linux Mint 18 Xfce. As shown in the picture below by the red arrows, how can I decrease the width of the gray zones that are to the left/right of each Emacs window? The so-called "padding", I guess.
Just turn off both the left and right fringe (the vertical gray bars you noticed).
M-x customize-option default-frame-alist, and add these entries, then save.
INS DEL Parameter: left-fringe Value: 0 INS DEL Parameter: right-fringe Value: 0
That adds these entries to the alist value of
(left-fringe . 0) (right-fringe . 0)
So for example, if the original value of your
()) then the new value after customization would be this:
((left-fringe . 0) (right-fringe . 0))
C-h v default-frame-alistshows you the current value and describes this option.
Another way: customize option
fringe-mode, setting it to
(0 . 0).
(I mention option
default-frame-alist first because it is a good thing to know. It lets you configure many other frame parameters, besides just the fringe.)
For more information, see the Emacs manual, node Fringes. You can find this node yourself, by asking Emacs about the fringe:
C-h r, then
i fringe TAB.