@media screen and (max-width: 1000px) {

    /* 中间内容 */
    .main {
        height: auto;
        padding: 20px 5%;
    }

    .main-list {
        width: 100%;
        height: auto;
    }

    .main-list li {
        margin-bottom: 20px;
        margin-right: 1.2%;
    }

}

@media screen and (max-width: 500px) {

    /* 中间内容 */
    .main-list li {
        width: 48%;
        margin-right: 4%;
    }

    .main-list li:nth-child(2n) {
        margin-right: 0;
    }

}