* {
    box-sizing: border-box;
}

html {
    font-size: 62.5%;
}

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

.trand {
    position: relative;
    height: 30px;
    width: 20px;
}

.top,
.bottom {
    background-color: #000;
    position: absolute;
    border-radius: 50%;
    animation: move 3s ease-in-out infinite;
}

.trand:nth-child(1) .top {
    animation-delay: 0s;
}
.trand:nth-child(1) .bottom {
    animation-delay: 1.5s;
}

.trand:nth-child(2) .top {
    animation-delay: 0.2s;
}
.trand:nth-child(2) .bottom {
    animation-delay: 1.7s;
}

.trand:nth-child(3) .top {
    animation-delay: 0.4s;
}
.trand:nth-child(3) .bottom {
    animation-delay: 1.9s;
}

.trand:nth-child(4) .top {
    animation-delay: 0.6s;
}
.trand:nth-child(4) .bottom {
    animation-delay: 2.1s;
}

.trand:nth-child(5) .top {
    animation-delay: 0.8s;
}
.trand:nth-child(5) .bottom {
    animation-delay: 2.3s;
}

.trand:nth-child(6) .top {
    animation-delay: 1s;
}
.trand:nth-child(6) .bottom {
    animation-delay: 2.5s;
}

.trand:nth-child(7) .top {
    animation-delay: 1.2s;
}
.trand:nth-child(7) .bottom {
    animation-delay: 2.7s;
}

@keyframes move {
    0% {
        top: 100%;
        z-index: -3;
    }
    25% {
        height: 8px;
        width: 8px;
        z-index: -3;
        opacity: 0;
    }

    50% {
        top: 0%;
        z-index: -3;
    }
    75% {
        height: 12px;
        width: 12px;
        z-index: 3;
    }
    100% {
        top: 100%;
        z-index: 3;
    }
}