Variable: tool-bar-button-margin
tool-bar-button-margin is a variable defined in xdisp.c.
Value
4
Documentation
Margin around tool-bar buttons in pixels.
If an integer, use that for both horizontal and vertical margins.
Otherwise, value should be a pair of integers (HORZ . VERT) with
HORZ specifying the horizontal margin, and VERT specifying the
vertical margin.
Probably introduced at or before Emacs version 21.1.
Source Code
// Defined in /usr/src/emacs/src/xdisp.c
DEFVAR_LISP ("tool-bar-button-margin", Vtool_bar_button_margin,
doc: /* Margin around tool-bar buttons in pixels.
If an integer, use that for both horizontal and vertical margins.
Otherwise, value should be a pair of integers `(HORZ . VERT)' with
HORZ specifying the horizontal margin, and VERT specifying the
vertical margin. */);