@media only screen and (min-height: 481px) and (max-height: 720px) {
    header {
        height: 5%;
    }

    content {
        top: 5%;
        bottom: 5%;
    }

    footer {
        height: 5%;
    }

    .content_left {
        display: none;
    }

    .content_right {
        display: none;
    }

    .content_main {
        width: 100%;
    }

    .menu {
        height: auto;
        width: 100%;
    }

    content ul li {
        width: calc((100% - 20px)/2);
    }
}

@media only screen and (min-width: 481px) and (max-width: 720px) {

    header {
        height: 10%;
    }

    content {
        top: 10%;
        bottom: 10%;
    }

    footer {
        height: 10%;
    }

    .menu {
        height: auto;
        width: 100%;
    }

    .content_left {
        display: none;
    }

    .content_right {
        display: none;
    }

    .content_main {
        width: 100%;
    }

    content ul li {
        width: calc((100% - 20px)/2);
    }
}