cssでスライダー

<div class="slide inner">
  <div class="box"></div>
  <div class="box"></div>
  <div class="box"></div>
</div>

.slide {
  overflow-x: scroll;★ 
  white-space: nowrap;★
}

.inner {
  max-width: 1000px;
  margin: 0 auto;
}

.box {
  display: inline-block;★ 
  width: 400px;
  height: 400px;
  background-color: black;
  margin-right: 20px;
}