:root {
            --primary: #0066cc;
            --bg: #f8fafd;
            --white: #ffffff;
            --text-main: #222222;
            --text-sub: #666666;
            --border: #e8ecef;
            --radius: 16px;
            --shadow: 0 10px 30px rgba(0,0,0,0.06);
        }

        * { box-sizing: border-box; margin: 0; padding: 0; }
        body {
            font-family: 'Noto Sans JP', sans-serif;
            background-color: var(--bg);
            color: var(--text-main);
            line-height: 1.8;
        }
        a { text-decoration: none; color: inherit; transition: 0.3s; }
        ul { list-style: none; }

        .site-header { background: var(--white); border-bottom: 1px solid var(--border); z-index: 1000; }
        .header-inner { max-width: 1200px; margin: 0 auto; padding: 15px 20px; display: flex; align-items: center; }
        .logo img { height: 28px; display: block; }

        .g-nav { background: var(--white); border-bottom: 1px solid var(--border); }
        .g-nav ul { max-width: 1200px; margin: 0 auto; display: flex; padding: 0 10px; }
        .g-nav li a { display: block; padding: 14px 15px; font-size: 14px; font-weight: 500; color: var(--text-sub); }

        .main-layout { max-width: 1200px; margin: 40px auto; padding: 0 20px; display: flex; gap: 50px; }
        aside { flex: 0 0 220px; }
        .sidebar-item { margin-bottom: 35px; }
        .sidebar-item h2 {
            font-size: 14px; font-weight: 700; margin-bottom: 15px; padding-bottom: 8px;
            border-bottom: 2px solid var(--border); position: relative; color: var(--text-sub);
        }
        .sidebar-item h2::after {
            content: ''; position: absolute; bottom: -2px; left: 0; width: 30px; height: 2px; background: var(--primary);
        }
        .sidebar-list li a { display: block; padding: 6px 0; font-size: 14px; }

        main { flex: 1; min-width: 0; }
        .section-title { font-size: 24px; font-weight: 700; margin-bottom: 30px; display: flex; align-items: center; gap: 15px; }
        .section-title::after { content: ''; flex: 1; height: 1px; background: var(--border); }

        .event-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(320px, 1fr)); gap: 30px; }
        .event-card {
            background: var(--white); border-radius: var(--radius); overflow: hidden;
            box-shadow: var(--shadow); border: 1px solid rgba(0,0,0,0.03);
            display: flex; flex-direction: column;
        }
        .card-img-wrapper { width: 100%; background: #f0f0f0; display: flex; align-items: center; justify-content: center; position: relative; }
        .card-img { max-width: 100%; max-height: 100%; object-fit: contain; display: block; }
        .card-body { padding: 30px; flex-grow: 1; }
        .card-date { 
            display: inline-block; font-size: 12px; font-weight: 700; color: var(--primary); margin-bottom: 10px; 
            background: rgba(0,102,204,0.06); padding: 2px 10px; border-radius: 4px; 
            font-size: 16px;
        }
        .card-topic { font-size: 20px; font-weight: 700; margin-bottom: 15px; line-height: 1.5; color: #000; }
        .card-note { font-size: 16px; color: var(--text-main); line-height: 1.9; }

        @media (min-width: 769px) {
            .event-grid.is-single { display: block; }
            .event-grid.is-single .event-card { flex-direction: row; align-items: flex-start; background: transparent; box-shadow: none; border: none; }
            .event-grid.is-single .card-img-wrapper {
                flex: 0 0 420px; position: sticky; top: 20px; 
                max-height: 90vh; border-radius: var(--radius); box-shadow: var(--shadow);
                background: #fff; padding: 10px; border: 1px solid var(--border);
            }
            .event-grid.is-single .card-body { flex: 1; padding: 0 0 0 50px; }
        }

        /* --- アーカイブ共通設定 --- */
        .past-events { margin-top: 80px; }

        /* 外側の折りたたみ（「過去のアーカイブを表示する」ボタン） */
        .archive-container-toggle { border: none; background: transparent; }
        .archive-container-toggle > summary {
            background: #eee; border-radius: 8px; display: flex;
            justify-content: center; align-items: center;
            padding: 15px; font-weight: bold; color: var(--text-sub); 
            list-style: none; cursor: pointer; transition: background 0.3s;
        }
        .archive-container-toggle > summary::-webkit-details-marker { display: none; }
        .archive-container-toggle > summary:hover { background: #e5e5e5; }

        /* 開いている時のボタンのデザインとテキスト */
        .archive-container-toggle[open] > summary {
            background: #ddd; margin-bottom: 20px;
        }
        .archive-container-toggle[open] > summary::after { content: "を閉じる"; margin-left: 5px; }

        /* 開いていない時は中身（タイトルとリスト）を隠す */
        .archive-container-toggle:not([open]) > .section-title,
        .archive-container-toggle:not([open]) > .archive-item {
            display: none;
        }

        /* 個別のアーカイブアイテム */
        .archive-item { background: var(--white); margin-bottom: 10px; border-radius: 10px; border: 1px solid var(--border); }
        .archive-item summary { padding: 18px 25px; cursor: pointer; font-weight: 500; display: flex; justify-content: space-between; align-items: center; }
        .archive-body { padding: 25px; border-top: 1px solid var(--border); font-size: 14px; background: #fafbfc; }

        footer { background: #1a1a1a; color: #fff; padding: 60px 20px 40px; margin-top: 100px; }
        .footer-inner { max-width: 1200px; margin: 0 auto; text-align: center; }
        .footer-logo img { height: 26px; filter: brightness(0) invert(1); margin-bottom: 30px; }
        .footer-links { margin-bottom: 30px; display: flex; justify-content: center; flex-wrap: wrap; gap: 15px 25px; }
        .footer-links a { color: #888; font-size: 13px; }
        .copy { font-size: 11px; color: #444; margin-top: 40px; border-top: 1px solid #222; padding-top: 30px; }

        @media (max-width: 768px) {
            .g-nav { display: none; }
            .main-layout { flex-direction: column; margin: 20px auto; }
            main { order: 1; }
            aside { order: 2; margin-top: 40px; padding-top: 30px; border-top: 1px solid var(--border); }
            .card-img-wrapper { height: auto; min-height: 50px; padding: px; }
            .card-img { width: 100%; height: auto; }
            .mobile-footer-nav { display: block; margin-bottom: 40px; padding-bottom: 30px; border-bottom: 1px solid #222; }
            .mobile-footer-nav ul { display: flex; flex-direction: column; gap: 15px; }
            .mobile-footer-nav a { color: #ccc; font-size: 14px; }
        }
        @media (min-width: 769px) { .mobile-footer-nav { display: none; } }