Body height 100% displaying vertical scrollbar

Question

Out of curiosity, considering the example below, why does having the margin on the #container div cause a vertical scrollbar to appear in the browser? The container is much

Answer 1

/*removes default margin & padding*/
html, body{
    padding: 0px !important;
    margin: 0px !important;
}

/*sets body height to max; and allows scrollbar as page content grows*/
body{
    min-height: 100vh;
}