table {
    margin: auto;
    text-align: center;
}

td {
    padding: 2em;
}
div.image-holder
{
    height: 180px;
}
.helper {
    display: inline-block;
    height: 100%;
    vertical-align: middle;
}
div.image-holder img {
    border: thin #ccc solid;
    vertical-align: middle;
    padding: 0.5em;
}
h1{
    text-align: center;
}
a {
    text-decoration: none;
}
a:link{
    color: mediumblue;
}
a:link img{    
    border-width: thin;
}
a:visited{
    color: mediumblue;
}
a:visited img{
    border-width: thin;
}
a:hover{
    color: green;
}
a:hover img{
    border-color: green;
    border-width: 2px;
}
a:active {
    color: red;
}
a:active img{
    border-color: red;
    border-width: 2px;
}