:root {
    --primary-color: #4A9FD4;
    --primary-dark: #3a7fa8;
    --secondary-color: #10b981;
    --accent-color: #4A9FD4;
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-accent: #f3f4f6;
    --border-color: #e5e7eb;
    --error-color: #ef4444;
    --success-color: #10b981;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
}

/* ヘッダー */
.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    box-shadow: var(--shadow-sm);
    z-index: 1000;
    transition: all 0.3s ease;
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem 10%;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.logo-link {
    text-decoration: none;
    color: inherit;
}

.logo-text {
    color: var(--primary-color);
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 2rem;
    margin-bottom: 0;
}

.nav-menu a {
    color: var(--text-primary);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s ease;
    position: relative;
}

.nav-menu a:hover {
    color: var(--primary-color);
}

.nav-menu a::after {
    content: '';
    position: absolute;
    bottom: -4px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--primary-color);
    transition: width 0.3s ease;
}

.nav-menu a:hover::after {
    width: 100%;
}

.menu-toggle {
    display: none;
    flex-direction: column;
    gap: 4px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 4px;
    width: 30px;
}

.menu-toggle span {
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    transition: all 0.3s ease;
}

#vk-mobile-nav-menu-btn {
    display: none;
}

/* オーバーレイ（スマホメニュー表示時・ヘッダー外なので viewport 全体に効く） */
.nav-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    width: 100dvw;
    height: 100dvh;
    min-width: 100%;
    min-height: 100%;
    background: rgba(0, 0, 0, 0.4);
    border: none;
    cursor: pointer;
    z-index: 999;
    padding: 0;
}

/* メニュー表示中は背面スクロール防止 */
body.menu-open {
    overflow: hidden;
}

/* レスポンシブデザイン */
@media (max-width: 768px) {
    .nav-overlay[aria-hidden="false"] {
        display: block;
    }

    .nav-container {
        padding: 1rem 10px;
    }
    .nav-menu {
        position: fixed;
        top: 70px;
        left: -100%;
        flex-direction: column;
        background: white;
        width: 100%;
        padding: 2rem;
        box-shadow: var(--shadow-lg);
        transition: left 0.3s ease;
        z-index: 1002;
    }

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

    .menu-toggle {
        display: flex;
        position: relative;
        z-index: 1003;
    }
}