.media {
    height: 210px;
    width: 100%;
    overflow: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    background: #f5f5f5;
}

.media img {
    height: 100%;
    /* 以容器高度為準，等比縮放 */
    width: auto;
    display: block;
    max-width: 100%;
    /* 避免寬度超出容器 */
}

.files-list li.item {
    width: calc((100% - 100px) / 4);
}

@media (max-width: 576px) {
    .media {
        height: 140px;
    }

    .files-list li.item {
        width: calc((100% - 100px) / 1);
    }

    .files-list {
        align-items: center;
        justify-content: center;
    }
}