You are trying to add a transition for height 100%. For some browsers, this is a bit complicated. Instead, try switching to max-height. Transitions to max-heightare usually a much better way to use transitions.
You will need to change the code as shown below:
height max-height -. 25px :
.menu-text {
color: white;
font-size: 1.8vw;
line-height: 4vw;
position: absolute;
width: 100%;
text-align: center;
transition: all 100ms linear;
bottom: 0;
border-bottom-left-radius: 20px;
border-bottom-right-radius: 20px;
background-color: rgba(0, 0, 0, 0.5);
height:100%;
max-height:25px;
}
max-height mouseover mouseout, :
$('#btn-adm2').on('mouseover', function (event) {
$('#btn-adm2 .menu-text').css('max-height', '100%');
});
$('#btn-adm2').on('mouseout', function (event) {
$('#btn-adm2 .menu-text').css('max-height', '25px');
});
→ http://jsfiddle.net/09ov6gn4/
, !!!