In theme/boost/scss/moodle/undo.less, there is the following code:

// Extends bootstrapbase/less/bootstrap/type.less

// to enable ol lists to use a larger number set.

ol {

    margin: 0 0 $line-height-base / 2 2.5em;

}

But line-height doesn't have units, so it ends up with:

margin: 0 0 .75 2.5em;

Which the browser might ignore because of the lack of a unit on the third number.

But, even if it was working it's not clear what it's doing. The comment suggests it's trying to increase the left margin, but it touches all of them, overwriting the bootstrap default for the bottom margin. Maybe it was based on code from Bootstrap 3 (the comment mentions .less files) but that value has changed since. So ideally it would just be deleted and leave the bootstrap defaults on ol tags.