/* header */

.rectangle {
    position: absolute;
    background: white;
}

.header_frame {
    position: fixed;
    z-index: 9990;
    align-items: center;
    width: 100vw;
    height: 100px;
}

.header_bg {
    width: 100%;
    height: 100%;
    position: absolute;
}

.header_bg.active {
    opacity: 1;
}

.header_icon {
    position: absolute;
    width: 200px;
    height: auto;
    z-index: 9999;
    margin: 10px;
}

.menu_btn {
    display: flex;
    flex-direction: column;
    width: 40px;
    height: 40px;
    cursor: pointer;
    z-index: 9999;
    top: 30px;
    padding: 10px;
    justify-content: space-between;
    background-color: white;
    border-radius: 5px;
    position: absolute;
    margin-right: 30px;
    right: 0;
}

.menu_btn span {
    height: 3px;
    background: black;
    border-radius: 2px;
    transition: 0.3s;
}

.menu {
    display: flex;
    flex-direction: column;
    background-image: url(https://gakuensai.cloudfree.jp/materials/main/intro_bg.jpeg);
    background-size: cover;
    background-repeat: no-repeat;
    background-color: rgba(255, 255, 255, 0.7);
    background-blend-mode: lighten;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    height: 100vh;
    padding: 100px 20px;
    overflow-y: auto;
    transform: translateY(-100vh);
    transition:
        transform 1s ease,
        opacity 1s ease;
    opacity: 0;
    font-size: 20px;
}

.menu a {
    color: #2b7397;
    text-decoration: none;
    padding: 10px 0;
    text-align: center;
    font-family: sans-serif;
}

.menu a:first-child {
    border-top: none;
}

.menu.active {
    transform: translateY(0);
    opacity: 1;
}

.menu_btn.active span:nth-child(1) {
    transform: rotate(45deg) translate(6px, 6px);
}

.menu_btn.active span:nth-child(2) {
    opacity: 0;
}

.menu_btn.active span:nth-child(3) {
    transform: rotate(-45deg) translate(6px, -6px);
}

.book1 {
    width: 40vw;
    position: absolute;
    left: -50px;
    top: 300px;
}

.book2 {
    width: 40vw;
    height: auto;
    position: absolute;
    right: -50px;
    top: 300px;
    transform: rotateY(180deg);
}

.book3 {
    width: 70vw;
    height: auto;
    position: absolute;
    left: 16vw;
    top: 600px;
}

/* 携帯向け要素 */

@media (max-width: 480px) {
    .header_icon {
        position: absolute;
        width: 150px;
        height: auto;
        z-index: 9999;
        margin: 10px;
    }
}