styles.css

*{
    margin: 0;
    padding: 0;
    font-family: 'Poppins', sans-serif;
    box-sizing: border-box;
}

body{
    background: #2e364a;
}

.timeline{
    position: relative;
    max-width: 75em;
    margin: 100px auto;
}

.container{
    padding: 10px 50px;
    position: relative;
    width: 50%;
    /* background: rgba(0, 0, 0, 0.3); just for our help */
    animation: movedown 1s linear forwards;
    opacity: 0;
}
/* Animation keyframes */
@keyframes movedown {
    0%{
        opacity: 1;
        transform: translateY(-30%);
    }
    100%{
        opacity: 1;
        transform: translateY(0px);
    }
}
/* Putting animation delay for each child */
.container:nth-child(1){
    animation-delay: 0s;
}
.container:nth-child(2){
    animation-delay: 1s;
}
.container:nth-child(3){
    animation-delay: 2s;
}
.container:nth-child(4){
    animation-delay: 3s;
}
.container:nth-child(5){
    animation-delay: 4s;
}
.container:nth-child(6){
    animation-delay: 5s;
}

.text-box{
    padding: 20px 30px;
    background: #fff;
    position: relative;
    border-radius: 6px;
    font-size: 15px;
}

.left-container{
    left: 0;
}

.right-container{
    left: 50%;
}

.container img{
    position: absolute;
    width: 40px;
    border-radius: 50%;
    right: -20px;
    top: 32px;
    z-index: 10;
}

.right-container img{
    left: -20px;
}

.timeline::after{
    content: " ";
    position: absolute;
    width: 6px;
    height: 100%;
    background: #fff;
    top: 0;
    left: 50%;
    margin-left: -3px;
    z-index: -1;
    animation: moveline 6s linear forwards; 
    /* 6 seconds because we have 6 childs so 1s for each */
}
/* Animations keyframes */
@keyframes moveline {
    0%{
        height: 0;
    }
    100%{
        height: 100%;
    }
}

.text-box h2{
    font-weight: 600;
}

.text-box small{
    display: inline-block;
    margin-bottom: 15px;
}

.left-container-arrow{
    height: 0;
    width: 0;
    position: absolute;
    top: 28px;
    z-index: 1;
    border-top: 15px solid transparent;
    border-bottom: 15px solid transparent;
    border-left: 15px solid #fff;
    right: -14px;
}

.right-container-arrow{
    height: 0;
    width: 0;
    position: absolute;
    top: 28px;
    z-index: 1;
    border-top: 15px solid transparent;
    border-bottom: 15px solid transparent;
    border-right: 15px solid #fff;
    left: -14px;
}

/* Responsive Design */
@media screen and (max-width: 600px) {
    .timeline{
        margin: 50px auto;
    }
    .timeline::after{
        left: 31px;
    }
    .container{
        width: 100%;
        padding-left: 80px;
        padding-right: 25px;
    }
    .text-box{
        font-size: 13px;
    }
    .text-box small{
        margin-bottom: 10px;
    }
    .right-container{
        left: 0;
    }
    .left-container img, .right-container img{
        left: 10px;
    }
    .left-container-arrow, .right-container-arrow{
        border-right: 15px solid #fff;
        border-left: 0;
        left: -14px;
    }
}