button question:why are they have same margin-top

.button {
display:inline-block;  border: 1px solid #FFAAAA; background: #FFEEEE;
color: #FF6666; font-weight:bold;
box-shadow: 5px 5px 0px 0 #000; margin: 0 5px 5px 0;
}
.button:active { box-shadow:none; margin: 5px 0 0 5px; }