body {
    padding: 0;
    margin: 0;
    height: 100vh;
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
}

#challenge21 .container {
    position: relative;
    display: flex;
    justify-content: space-between;
}

#challenge21 .container span {
    position: relative;
    display: inline-block;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    background-color: #00bedf;
    margin: 0 5px;
    animation: quicking-balls linear infinite alternate-reverse 1s, change-color linear infinite 2s;
}

#challenge21 .container span:nth-child(2) {
    animation-delay: 0.2s
}

#challenge21 .container span:nth-child(3) {
    animation-delay: 0.4s
}

#challenge21 .container span:nth-child(4) {
    animation-delay: 0.6s
}

#challenge21 .container span:nth-child(5) {
    animation-delay: 0.8s
}

#challenge21 .container span:nth-child(6) {
    animation-delay: 1s
}

@keyframes quicking-balls {
    0% {
        transform: translateY(0)
    }
    50% {
        transform: translateY(-100px)
    }
    100% {
        transform: translateY(0)
    }
}

@keyframes change-color {
    0% {
        background-color: #00bedf;
    }
    25% {
        background-color: #00df38;
    }
    50% {
        background-color: #dfa400;;
    }
    75% {
        background-color: #df0086;
    }
    100% {
        background-color: #00bedf;
    }
}