@media only screen and (max-width: 640px) {
    
    .slider_h {
        font-size: 25px;
        letter-spacing: 1.5px;
        line-height: 30px;
    }
    .carousel-caption {
        bottom: 25%;
        left: 15%;
        right: 15%;
    }
    .banner_h{
        text-align: center;
        font-size: 40px;
        line-height: 45px;
    }
    #back {
        padding-top: 60px;
        padding-bottom: 60px;
    }
    .m_pb{
        margin-bottom: 30px;
    }
    .form_h{
        letter-spacing: 0;
    }
}