body {
  background: #efedd8;
  margin: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  overflow-x: hidden;
}

.box {
  margin: 10px;
  width: 400px;
  height: 200px;
  background: steelblue;
  color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
  box-shadow: 2px 4px 5px rgba(0, 0, 0, 0.3);
  border-radius: 10px;
  transform: translateX(200%);
  transition: all 0.5s;
  opacity: 0;
}

.box:nth-of-type(even) {
  transform: translateX(-200%);
}

.box.show {
  transform: translateX(0px);
  opacity: 1;
}

.trigger {
  width: 100%;
  height: 1px;
  background: #000;
  position: fixed;
  top: 50%;
}

.trigger::after {
  content: 'Trigger';
  position: absolute;
}