element-plus/website/demo-styles/date-picker.scss

.demo-block.demo-date-picker .source > div {
  padding: 0;
  display: flex;
  flex-wrap: wrap;
}

.demo-date-picker .block {
  padding: 30px 0;
  text-align: center;
  border-right: solid 1px var(--el-border-color-base);
  flex: 1;
  &:last-child {
    border-right: none;
  }
}

.demo-date-picker .container {
  flex: 1;
  border-right: solid 1px var(--el-border-color-base);
  .block {
    border-right: none;
    &:last-child {
      border-top: solid 1px var(--el-border-color-base);
    }
  }
  &:last-child {
    border-right: none;
  }
}

.demo-date-picker .demonstration {
  display: block;
  color: var(--el-text-color-secondary);
  font-size: 14px;
  margin-bottom: 20px;
}