bwj_wechat/components/My_inputPromptd/index.wxss

.tips_box {
    position: relative;
    padding: 10rpx;
    width: 240rpx;
    background-color: #ffffff;
    border-radius: 20rpx;
    opacity: .7;
}

.tips_box::after {
    position: absolute;
    content: '';
    display: block;
    border-top: 10px solid #ffffff;
    border-left: 10px solid transparent;
    border-right: 10px solid transparent;
    border-bottom: 10px solid transparent;
    bottom:-18px;
    left: 50%;
    transform: translate(-50%,0);
}