小编lx4*_*x4r的帖子

.top {
  background-color: green;
  height: 100px;
  width: 100%;
}
.bottom {
  background-color: red;
  height: 200px;
  width: 100%;
}
.triangle {
  border-top: 40px solid black;
  border-left: 950px solid transparent;
  border-right: 950px solid transparent;
  width: 0;
  height: 0;
  top: 107px;
  content: "";
  display: block;
  position: absolute;
  overflow: hidden;
  left: 0;
  right: 0;
  margin: auto;
}

<div class="top">
  <div class="triangle"></div>
</div>
<div class="bottom"></div>