HTML input button css-height not working on Safari and Chrome

Change it from <input> to <button> and add -webkit-appearance: none; to the start of your CSS, eg:

.submitbtn {
    -webkit-appearance: none;
    height: 50px;
    background-color:#FFF;
    color:#666;
    font-weight:bold;
    border: solid #666 1px;
    font-size: 14px;
}