Last I had to modify a custom page in SharePoint. I added some css but the hyperlinks always get the default markup. To overwrite the default markup I used the important keyword:
<style type="text/css">
.navigationText{
text-decoration:none !important;
color:#676767 !important;
width: 125px;
height: 125px;
display:table-cell;
font-size: medium;
text-align: center;
background-color: #CCEBFF;
vertical-align:middle;
}
</style>
More information about this keyword is on the W3.org website.