* {
    margin: 0;
    padding: 0;
}

h3 {
    width: 960px;
    height: 50px;
    background: #ccc;
    color: #000;
    text-align: center;
    line-height: 50px;
    margin-bottom: 10px;
}
.main {
    width: 960px;
    margin: 10px auto;
    overflow: hidden;
}

.left {
    width: 630px;
    height: 300px;
    background: #f00;
    float: left;
}
.right {
    width: 320px;
    height: 300px;
    background: #00f;
    float: right;
}

#imgBox {
    width: 960px;
    height: 500px;
    background: url("../img/1.jpg");
    background-repeat: no-repeat;
    background-size: cover;
}

@media screen and (max-width:480px) {
    #imgBox {
        width: 100%;
        height: 0px;
        padding-top: 58%;
        background: url(../img/3.jpg);
        background-repeat: no-repeat;
        background-size: contain;
    }
    h3 {
        width: 100%;
    }
    .main {
        width: 100%;
    }
    .left {
        width: 100%;
    }
    .right {
        width: 100%;
    }
}
@media screen and (min-width:960px) {
    #imgBox {
        width: 100%;
        height: 0px;
        padding-top: 58%;
        background: url(../img/2.jpg);
        background-repeat: no-repeat;
        background-size: contain;
    }
    h3 {
        width: 100%;
    }
    .main {
        width: 100%;
    }
    .left {
        width: 63%;
    }
    .right {
        width: 34%;
    }
}