335036 (1) [Avatar] Offline
In listing 7.6 the dropdown menu is absolutely positioning below the label using the following ruleset:
.dropdown-menu {
display: none;
position: absolute;
left: 0;
top: 2.1em;
min-width: 100%;
background-color: #eee;

Using top: 2.1em relays over the size of the dropdown label and the padding around it (.5em top and bottom).
Generally I think that using top: calc(100% + .1em) is a more solid approach as it allows to change the padding / font size freely