Using CSS:

.button {
    display: block;
    width: 115px;
    height: 25px;
    background: #4E9CAF;
    padding: 10px;
    text-align: center;
    border-radius: 5px;
    color: white;
    font-weight: bold;
    line-height: 25px;
}

<a class="button">Add Problem</a>

http://jsfiddle.net/GCwQu/