The triangle css part of el-popover

<div class="self-popover">
  <div class="self-arrow"></div>
</div>

.self-popover {
  width: 320px;
  height: 400px;
  position: absolute;
  right: -10px;
  top: 45px;
  background-color: #fff;
  box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
  border-radius: 8px;
  border: 1px solid #ebeef5;
  z-index: 20;

  .self-arrow {
    display: block;
    width: 0;
    height: 0;
    position: absolute;
    top: -12px;
    right: 7px;
    margin-right: 6px;
    border-color: transparent;
    border-style: solid;
    border-width: 12px;
    filter: drop-shadow(0 2px 12px rgba(0, 0, 0, 0.03));
    border-top-width: 0;
    border-bottom-color: #ebeef5;
    &::after {
      position: absolute;
      display: block;
      width: 0;
      height: 0;
      border-color: transparent;
      border-style: solid;
      border-width: 12px;
      content: " ";
      top: 1px;
      margin-left: -12px;
      border-top-width: 0;
      border-bottom-color: #ffffff;
    }
  }
}