您可能可以通过根据this ::before technique修改div border-radius值来更接近您要查找的内容。
Here is the result of the below code

<div class="container">
         <div class="left"></div>
         <div class="center"></div>
         <div class="right"></div>
    </div>

.container {
      display: flex;
    }
    .container div {
      height: 260px;
      width: 50px;
    }
    .center {
      position: relative;
      top: 10px;
      background-color: black;
      width: 55px !important;
      height: 250px !important;
    }
    .left::before {
      display: block;
      position: relative;
      content: "";
      width: 100%;
      height: 100%;
      background-color: black;
      border-radius: 0.8em 0.8em 0 0.8em;
    }
    .center::before {
      display: block;
      position: relative;
      content: "";
      width: 100%;
      height: 10%;
      background-color: white;
      border-radius: 0 0 40em 40em;
    }
    .right::before {
      display: block;
      position: relative;
      content: "";
      width: 100%;
      height: 100%;
      background-color: black;
      border-radius: 0.8em 0.8em 0.8em 0;
    }