markInsets property
The insets applied around the check mark when the checkbox is checked or in its indeterminate (tristate) state.
This insets the check mark inward; the size of the checkbox box itself
is not affected. The check mark and its stroke shrink to fit the
remaining space, so the mark stays proportional. Its size is the smaller
of the remaining width and height, and it is centered in the remaining
space, so an inset on one axis also shrinks it on the other. For example,
EdgeInsets.only(left: 9.0) draws a half-size mark centered in the right
half of the box.
On iOS and macOS, when using Checkbox.adaptive, this property has no effect, because the checkbox delegates to CupertinoCheckbox, which does not support insets.
Must be non-negative. If the horizontal or vertical insets are greater than or equal to the checkbox size, the check mark or indeterminate dash is not painted.
If null, CheckboxThemeData.markInsets is used. If that is also null, it defaults to EdgeInsets.zero and the check mark renders at full size.
Implementation
final EdgeInsets? markInsets;