timeline.css

/**
 * Timeline
 */
.timeline {
  list-style: none;
  margin-left: 1em;
  padding-bottom: 1em;
  /**
     * Line
     */
}

.timeline::before {
  content: '';
  position: absolute;
  top: 0.8em;
  left: 0;
  bottom: 0;
  width: 0.15em;
  background: #ddd;
}

.timeline-event {
  padding-left: 0.75em;
  /**
         * Circle
         */
}

.timeline-event:not(:last-child) {
  margin-bottom: .25em;
}

.timeline-event:hover .timeline-event-date {
  background: navy;
  color: #fff;
}

.timeline-event:hover .timeline-event-date::before {
  border-right-color: navy;
}

.timeline-event:hover::before {
  background: navy;
}

.timeline-event::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  border-radius: 100%;
  width: 0.5em;
  height: 0.5em;
  background: #999;
  border: 0.15em solid #eee;
  margin-left: -0.28571em;
  margin-top: 0.4em;
}

.timeline-event::after {
  content: '';
  display: table;
  clear: both;
}

.timeline-event-date {
  float: left;
  background: #666;
  color: #fff;
  border-radius: 2px;
  padding: 0 .35em;
  margin-right: 1em;
  margin-left: .3em;
}

.timeline-event-date::before {
  content: '';
  position: absolute;
  width: 0;
  height: 0;
  top: 50%;
  left: -.3em;
  margin-top: -.3em;
  border-right: 0.3em solid #666;
  border-top: .3em solid transparent;
  border-bottom: .3em solid transparent;
}

.timeline-event-title {
  float: left;
}