*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font: normal 16px/1.5 "Helvetica Neue", sans-serif;
  background: #456990;
  color: #fff;
  overflow-x: hidden;
  padding-bottom: 50px;
}  /* INTRO SECTION
–––––––––––––––––––––––––––––––––––––––––––––––––– */

.intro {
  background: #F45B69;
  padding: 100px 0;
}

.container {
  width: 90%;
  max-width: 1200px;
  margin: 0 auto;
  text-align: center;
}

h1 {
  font-size: 2.5rem;
}


/* TIMELINE
–––––––––––––––––––––––––––––––––––––––––––––––––– */

.timeline ul {
  background: #456990;
  padding: 50px 0;
}

.timeline ul li {
  list-style-type: none;
  position: relative;
  width: 6px;
  margin: 0 auto;
  padding-top: 50px;
  background: #fff;
}

.timeline ul li::after {
  content: '';
  position: absolute;
  left: 50%;
  bottom: 0;
  transform: translateX(-50%);
  width: 30px;
  height: 30px;
  border-radius: 50%;
  background: inherit;
}

.timeline ul li div {
  position: relative;
  bottom: 0;
  width: 400px;
  padding: 15px;
  background: #F45B69;
}

.timeline ul li div::before {
  content: '';
  position: absolute;
  bottom: 7px;
  width: 0;
  height: 0;
  border-style: solid;
}

.timeline ul li:nth-child(odd) div {
  left: 45px;
}

.timeline ul li:nth-child(odd) div::before {
  left: -15px;
  border-width: 8px 16px 8px 0;
  border-color: transparent #F45B69 transparent transparent;
}

.timeline ul li:nth-child(even) div {
  left: -439px;
}

.timeline ul li:nth-child(even) div::before {
  right: -15px;
  border-width: 8px 0 8px 16px;
  border-color: transparent transparent transparent #F45B69;
}

time {
  display: block;
  font-size: 1.2rem;
  font-weight: bold;
  margin-bottom: 8px;
}


/* EFFECTS
–––––––––––––––––––––––––––––––––––––––––––––––––– */

.timeline ul li::after {
  transition: background .5s ease-in-out;
}

.timeline ul li.in-view::after {
  background: #F45B69;
}

.timeline ul li div {
  visibility: hidden;
  opacity: 0;
  transition: all .5s ease-in-out;
}

.timeline ul li:nth-child(odd) div {
  transform: translate3d(200px, 0, 0);
}

.timeline ul li:nth-child(even) div {
  transform: translate3d(-200px, 0, 0);
}

.timeline ul li.in-view div {
  transform: none;
  visibility: visible;
  opacity: 1;
}


/* GENERAL MEDIA QUERIES
–––––––––––––––––––––––––––––––––––––––––––––––––– */

@media screen and (max-width: 900px) {
  .timeline ul li div {
    width: 250px;
  }
  .timeline ul li:nth-child(even) div {
    left: -289px;
    /*250+45-6*/
  }
}

@media screen and (max-width: 600px) {
  .timeline ul li {
    margin-left: 20px;
  }
  .timeline ul li div {
    width: calc(100vw - 91px);
  }
  .timeline ul li:nth-child(even) div {
    left: 45px;
  }
  .timeline ul li:nth-child(even) div::before {
    left: -15px;
    border-width: 8px 16px 8px 0;
    border-color: transparent #F45B69 transparent transparent;
  }
}

(function() {

  'use strict';

  // define variables
  var items = document.querySelectorAll(".timeline li");

  // check if an element is in viewport
  // http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
  function isElementInViewport(el) {
    var rect = el.getBoundingClientRect();
    return (
      rect.top >= 0 &&
      rect.left >= 0 &&
      rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
      rect.right <= (window.innerWidth || document.documentElement.clientWidth)
    );
  }

  function callbackFunc() {
    for (var i = 0; i < items.length; i++) {
      if (isElementInViewport(items[i])) {
        items[i].classList.add("in-view");
      }
    }
  }

  // listen for events
  window.addEventListener("load", callbackFunc);
  window.addEventListener("resize", callbackFunc);
  window.addEventListener("scroll", callbackFunc);

})();





Resources

<section class="intro">
  <div class="container">
    <h1>Vertical Timeline &darr;</h1>
  </div>
</section>

<section class="timeline">
  <ul>
    <li>
      <div>
        <time>1934</time> At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium
      </div>
    </li>
    <li>
      <div>
        <time>1937</time> Proin quam velit, efficitur vel neque vitae, rhoncus commodo mi. Suspendisse finibus mauris et bibendum molestie. Aenean ex augue, varius et pulvinar in, pretium non nisi.
      </div>
    </li>
    <li>
      <div>
        <time>1940</time> Proin iaculis, nibh eget efficitur varius, libero tellus porta dolor, at pulvinar tortor ex eget ligula. Integer eu dapibus arcu, sit amet sollicitudin eros.
      </div>
    </li>
    <li>
      <div>
        <time>1943</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
    <li>
      <div>
        <time>1946</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
    <li>
      <div>
        <time>1956</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
    <li>
      <div>
        <time>1957</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
    <li>
      <div>
        <time>1967</time> Aenean condimentum odio a bibendum rhoncus. Ut mauris felis, volutpat eget porta faucibus, euismod quis ante.
      </div>
    </li>
    <li>
      <div>
        <time>1977</time> Vestibulum porttitor lorem sed pharetra dignissim. Nulla maximus, dui a tristique iaculis, quam dolor convallis enim, non dignissim ligula ipsum a turpis.
      </div>
    </li>
    <li>
      <div>
        <time>1985</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
    <li>
      <div>
        <time>2000</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
    <li>
      <div>
        <time>2005</time> In mattis elit vitae odio posuere, nec maximus massa varius. Suspendisse varius volutpat mattis. Vestibulum id magna est.
      </div>
    </li>
  </ul>
</section>