* {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.main {
    height: 2000px;
}

.btn {
    border: none;
    background-color: #0081cb;
    width: 40px;
    height: 40px;
    padding: 10px;
    position: fixed;
    bottom: 10px;
    right: 10px;
    color: #fff;
    display: none;
    cursor: pointer;
}