.header {
    display: none;
}
@media screen and (max-width: 980px) {

    /* ヘッダー（トップバー） */
    .header {
        top: 0%;
        display: block;
        position: fixed;
        width: 100%;
        z-index: 99;
        display: flex;
        justify-content: space-between;
        font-family: Orbitron, arial;
        align-items: center;
        background-color: #ffffff;
        font-size: 30px;
        /* 緑色 ＃00666 */
        color: white;
        padding: 10px 15px;
        height: 100px;
        box-sizing: border-box;
        background-image: url(../img/卒業生サイト画像/2024/ヘッダーロゴ.png);
        background-size: contain;
        background-repeat: no-repeat;
    }

    .logo-icons {
        display: flex;
        align-items: center;
        gap: 10px;
    }

    .icon {
        width: 80px;
        height: 80px;
        background-color: white;
        border-radius: 4px;
        display: flex;
        align-items: center;
        justify-content: center;
        font-size: 12px;
        color: #000;
    }

    .hamburger {
        width: 80px;
        height: 80px;
        background-color: transparent;
        border: none;
        cursor: pointer;
        position: relative;
    }

    .hamburger span {
        display: block;
        height: 3px;
        width: 100%;
        background-color: rgb(58, 58, 58);
        margin: 15px 0;
        transition: 0.3s;
    }

    /* オーバーレイ */
    .overlay {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background-color: rgba(0, 0, 0, 0.5);
        z-index: 98;
        opacity: 0;
        visibility: hidden;
        transition: opacity 0.3s, visibility 0.3s;
    }

    .overlay.active {
        opacity: 1;
        visibility: visible;
    }

    /* メニューコンテナ */
    .menu-container {
        font-family: Orbitron, arial;
        position: fixed;
        top: 0;
        left: -100%;
        width: 80%;
        /* max-width: 300px; */
        height: 100vh;
        background-color: #0099ff;
        z-index: 99;
        transition: left 0.3s ease-in-out;
        overflow-y: auto;
        padding: 10px 0 0 0;
        box-sizing: border-box;
    }

    .menu-container h2 {
        font-weight: 200;
        color: white;
        text-align: center;
    }

    .menu-container.active {
        left: 0;
    }

    /* メニュー項目 */
    .menu-item {
        border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    }

    .menu-link {
        display: flex;
        justify-content: space-between;
        align-items: center;
        padding: 15px;
        color: white;
        text-decoration: none;
        font-size: 30px;
        transition: background-color 0.2s;
    }

    .menu-link:hover {
        background-color: rgba(255, 255, 255, 0.1);
    }

    .expand-icon {
        width: 52px;
        height: 52px;
        background-color: transparent;
        font-family: arial;
        border: 1px solid white;
        /* border-radius: 50%; */
        display: flex;
        align-items: center;
        justify-content: center;
        font-size: 50px;
        padding: 2px;
        cursor: pointer;
        user-select: none;
    }

    .submenu {
        max-height: 0;
        overflow: hidden;
        transition: max-height 0.3s ease-out;
        background-color: rgba(0, 0, 0, 0.2);
    }

    .submenu.active {
        max-height: 100vh;
        /* 十分な高さ */
    }

    .submenu .menu-item {
        border-bottom: 1px solid rgba(255, 255, 255, 0.05);
    }

    .submenu .menu-link {
        padding-left: 30px;
        /* font-size: 30px; */
    }

    /* 特殊項目のビデオアイコン例 */
    .video-icon {
        width: 16px;
        height: 16px;
        background-color: white;
        border-radius: 2px;
        display: inline-flex;
        align-items: center;
        justify-content: center;
        font-size: 10px;
        color: #0099ff;
        margin-left: 5px;
    }

    /* MOREセクション */
    .more-section {
        padding: 15px;
        color: white;
        background-color: #0071ba;
    }
}