OK, accidentally I've mixed a few solutions, and it finally works now for my layout where I tried to make a 3x3 table with Bootstrap columns on the smallest resolution.
/* Required styles */
#grid a {
display: table;
}
#grid a div {
display: table-cell;
vertical-align: middle;
float: none;
}
/* Additional styles for demo: */
body {
padding: 20px;
}
a {
height: 40px;
border: 1px solid #444;
}
a > div {
width: 100%;
text-align: center;
}