如何使用CSS创建3列多边形容器

<div class="container"></div>

.container {
  width: 300px;
  height: 200px;
  position: relative;
}

.container::before,
.container::after {
  content: "";
  position: absolute;
  top: 0;
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 100px 0 100px 100px;
  border-color: transparent transparent transparent #000;
}

.container::before {
  left: -100px;
}

.container::after {
  right: -100px;
}

.container {
  background-color: #f1f1f1;
}

.container::before,
.container::after {
  background-color: #fff;
}

.container {
  border: 1px solid #ccc;
  box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
  border-radius: 5px;
}

.container::before,
.container::after {
  border-color: transparent transparent transparent #ccc;
}