<link href='https://fonts.googleapis.com/css?family=Montserrat' rel='stylesheet' type='text/css'>
<button>hover me!</button>

body {
    background-color: #111111;
    background-image: url('http://placekitten.com/1000/1000');
}
button {
    transition: all .5s ease;
    color: #fff;
    border: 3px solid white;
    font-family:'Montserrat', sans-serif;
    text-transform: uppercase;
    text-align: center;
    line-height: 1;
    font-size: 17px;
    background-color : transparent;
    padding: 10px;
    outline: none;
    border-radius: 4px;
}
button:hover {
    color: #001F3F;
    background-color: #fff;
}