style.css

body {
    background-color:black;
    margin : 0;
    overflow : hidden;
    font-family: 'Montserrat', sans-serif;
    font-family: 'Stint Ultra Condensed', cursive;
    font-family: 'Stint Ultra Expanded', cursive;
    font-family: 'Ultra', serif;
}

#panel {
    color : black;
    background-color: black;
    padding: 5px;
    text-align:center;
}

.btn {
    background-color: #1abc9c;
    color: black;
    outline-color: #1abc9c;
    outline-style: outset;
    border-radius: 25%;
    transition: 0.5s;
    padding: 15px;
    font-size: 20px;
    margin: 1px;
}

.btn:hover {
    background-color: #16a085;
    outline-color:#16a085;
    color: white;
    transition: 0.5s;
}

.btn:active {
    background-color: #16a085;
    outline-color: #16a085;
    color: white;
    outline-style: inset;
    transition: 0.5s;
}

#START {
    padding: 15px;
    font-size: 20px;
    background-color:#e74c3c;
    outline-color: #e74c3c;
}

#START:hover {
    background-color: #c0392b;
    outline-color:#c0392b;
    color: white;
    transition: 0.5s;
}

#START:active {
    background-color: #990000;
    outline-color: #990000;
    color: white;
    outline-style: inset;
    transition: 0.5s;
}