> What will that achieve? Isn’t 1em the default?
default is something like 1.4em
line-height:1em will reduce line height to font size so height of the element and its border will be the same with font size, but yes it will reduce ‘clickable’ area too (depends on what are you doing.. it’s just text links or it’s some kind of buttons with clickable area).
Anyway you can use right positioned background image for border and use data:image to save number of http requests ( https://css-tricks.com/data-uris/ )