Ah I may have forgotten one change.

Add the following CSS to .btn-secondary on line 235 of the style.css file.

background: transparent;

So it should look like this,

.btn-secondary {
    background: transparent;
    border-color: #e8e8e8;
    color: #e8e8e8;
    display: inline-block;
    text-decoration: none;
}