用cover-view画一个三角形，其他两条边框设置为透明色，底边框为白色，形成三角形背景，微信开发者工具能正常显示，手机上就不显示三角形

<cover-view class="triangle-cover">
    <cover-view class="triangle-content"></cover-view>
</cover-view>

.triangle-cover {
    position: relative;
    width: 100px;
    height: 36px;
    overflow: hidden;
}

.triangle-content {
    position: absolute;
    top: 0;
    left: 48px;
    width: 0;
    height: 0;
    border-left: 1px solid transparent;
    border-right: 12px solid transparent;
    border-top: 40px solid #fff;
}