@media screen and (max-width: 750px) {
    .m_activity_header {
        position: relative;
        padding: 0 0.3rem;
        height: 0.88rem;
        line-height: .88rem;
        background: #4475B7;
    }
    .m_activity_header .back_btn {
        position: absolute;
        left: .3rem;
        top: 50%;
        transform: translateY(-50%);
        width: .26rem;
        height: .41rem;
        background:url(../images/nav/back_btn.png) no-repeat;
        background-size: 100% 100%;
    }
    .m_activity_header h3 {
        text-align: center;
        font-size: .32rem;
        font-weight: 700;
    }
    .m_activity_header .home_btn {
        position: absolute;
        right: .3rem;
        top: 50%;
        transform: translateY(-50%);
        width: .64rem;
        height: .64rem;
        background:url(../images/nav/home_btn.png) no-repeat;
        background-size: 100% 100%;
    }
}