利用css3画三角形

<view class="sjx"></view>

<style>
.sjx{
        width: 0;
        height: 0;
        margin-top: 2rpx;
        margin-left:12%;
        border-width: 0 10rpx 10rpx 10rpx;
        border-style: solid;
        border-color: transparent transparent rgba(255, 0, 0, 1.0);
        transform:rotate(90deg);
    }
</style>