style.css

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

body{
    background: #2e364a;
}

.timeline{
    position: relative;
    max-width: 1200px;
    margin: 100px auto;
}

.container{
    padding: 10px 50px;
    position: relative;
    width: 50%;
    animation: movedown 1s linear forwards;
    opacity: 0;
}

@keyframes movedown{
    0%{
        opacity: 1;
        transform: translateY(-30px);
    }

    100%{
        opacity: 1;
        transform: translateY(-30px);
    }
}

.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;
}

@media screen and (max-width: 600px) {
    
    .timeline{
        margin: 50px auto;
    }

    .timeline::after{
        left: 31px;
    }
    
    .container{
        width: 100%;
        padding-left: 80px;
        padding-right: 25px;
    }

    .textbox{
        font-size: 13px;
    }

    .textbox 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: -15px;
    }
}

.textbox{
    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: white;
    top: 0;
    left: 50%;
    margin-left: -3px ;
    z-index: -1;
    animation: moveline 6s linear forwards;
}

@keyframes moveline {
    0%{
        height: 0;
    }

    100%{
        height: 100%;
    }
}

.textbox h2{
    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 rgb(255, 255, 255);
    right: -15px;
}

.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 rgb(255, 255, 255);
    left: -15px;
}