timeline.css

* {
  box-sizing: border-box;
}
/*Comments are given properly so that a even a "noob" can understand*/

/* The actual timeline (the vertical ruler) */
.timeline {
    position: relative;
    max-width: 1200px;
    margin: 0 auto;
}
/* The actual timeline (the vertical ruler) */
.timeline::after {
    content: '';
    position: absolute;
    width: 6px;
    background-color: white;
    top: 0;
    bottom: 0;
    left: 50%;
    margin-left: -3px;
}
/* Container around content */
.containerx {
    padding: 10px 40px;
    position: relative;
    background-color: inherit;
    width: 50%;
}
/* The circles on the timeline */
.containerx::after {
    content: '';
    position: absolute;
    width: 20px;
    height: 20px;
    right: -14px;
    background-color:#4d4b4b;
    border: 4px solid white;
    top: 15px;
    border-radius: 50%;
    z-index: 1;
}
/* Place the container to the left */
.left {
    left: 0;
}

/* Place the container to the right */
.right {
    left: 50%;
}
/* Add arrows to the left container (pointing right) */
.left::before {
    content: " ";
    height: 0;
    position: absolute;
    top: 22px;
    width: 0;
    z-index: 1;
    right: 30px;
    border: medium solid white;
    border-width: 10px 0 10px 10px;
    border-color: transparent transparent transparent white;
}
/* Add arrows to the right container (pointing left) */
.right::before {
    content: " ";
    height: 0;
    position: absolute;
    top: 22px;
    width: 0;
    z-index: 1;
    left: 30px;
    border: medium solid white;
    border-width: 10px 10px 10px 0;
    border-color: transparent white transparent transparent;
}
/* Fix the circle for containers on the right side */
.right::after {
    left: -16px;
}

/* The actual content */
.content {
    padding: 20px 30px;
    background-color: white;
    position: relative;
    border-radius: 6px;
}

/* Media queries - Responsive timeline on screens less than 600px wide */
@media screen and (max-width: 600px) {
  /* Place the timelime to the left */
  .timeline::after {
    left: 31px;
  }
  
  /* Full-width containers */
  .containerx {
    width: 100%;
    padding-left: 70px;
    padding-right: 25px;
  }
  
  /* Make sure that all arrows are pointing leftwards */
  .containerx::before {
    left: 60px;
    border: medium solid white;
    border-width: 10px 10px 10px 0;
    border-color: transparent white transparent transparent;
  }

  /* Make sure all circles are at the same spot */
  .left::after, .right::after {
    left: 15px;
  }
  
  /* Make all right containers behave like the left ones */
  .right {
    left: 0%;
  }