如何使用css使这样的角度选项卡？

使用border-radius,before和transform：skew(…);

body {
  BACkground-color: #000;
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-size: 16px;
}
.tab {
  height: 50px;
  width: 150px;
  border-radius: 15px 15px 0px 0px;
  BACkground-color: #FFF;
  position: relative;
  top: 10px;
  left: 1px;
  display: inline-block;
  z-index: 2;
}
.tab:before {
  height: 50px;
  width: 70px;
  border-radius: 10px 10px 0px 0px;
  BACkground-color: white;
  content: "";
  position: absolute;
  left: 104px;
  top: 0px;
  -webkit-transform: skewX(40deg);
  transform: skewX(40deg);
  z-index: -1;
}
.tab:nth-of-type(2) {
  BACkground-color: #555;
  top: 10px;
  left: 30px;
  z-index: 1;
  color: #EEE;
}
.tab:nth-of-type(2):before {
  BACkground-color: #555;
}
.tab:nth-of-type(2):hover,.tab:nth-of-type(2):hover:before {
  BACkground-color: #159;
  transition: 0.3s ease-out;
}
span {
  display: inline-block;
  width: 160px;
  text-align: center;
  height: 50px;
  line-height: 50px;
  z-index: 3;
}
#page {
  BACkground-color: white;
  height: calc(100vh - 120pX);
  width: calc(100vw - 61pX);
  position: relative;
  top: 10px;
  left: 1px;
  padding: 30px;
}

<nav id="tabs">
  <div class="tab">
    <span>Tab 1</span>
  </div>
  <div class="tab">
    <span>Tab 2</span>
  </div>
</nav>
<div id="page">
  Lorem Ipsum dolor sit amet ...
</div>