body{
    font-family: Arial, sans-serif;
    background-color: green;
    padding: 20px;
}
h2{
    text-align: center;
}
#tree{
    margin-top: 20px;
}
.branch{
    margin-left: 30px;
    margin-top: 10px;
    padding-left: 20px;
    border-left: 2px solid gray;
}
button{
    padding: 8px 15px;
    margin: 5px 0;
    background-color: violet;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: 0.2s;
}
button:hover{
    background-color: blue;
    transform: scale(1.05);
}
button:disabled{
    background-color: skyblue;
    cursor: default;
}
@keyframes fade{
    from{
        opacity: 0;
    }
    to{
        opacity: 1;
    }
}
.branch {
    animation: fade 0.4s;
}