@media (min-width: 1920px) {
    .content-container {
        max-width: 1400px;
    }

    .sidebar {
        width: 280px;
    }
}

@media (min-width: 1025px) and (max-width: 1366px) {
    .sidebar {
        width: 240px;
    }

    .main-content {
        padding: 36px;
    }

    .content-container {
        max-width: 1100px;
    }

    .overview-section {
        grid-template-columns: repeat(4, 1fr);
    }

    .home-grid {
        grid-template-columns: 1.5fr 1fr;
    }

    .study-options-grid {
        grid-template-columns: repeat(4, 1fr);
    }

    .items-grid,
    .friends-grid,
    .cards-grid,
    .practice-options,
    .games-grid {
        grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    }
}

@media (min-width: 769px) and (max-width: 1024px) {
    .sidebar {
        width: 200px;
    }

    .sidebar-logo {
        font-size: 16px;
    }

    .nav-item {
        font-size: 13px;
        padding: 10px 12px;
    }

    .nav-icon {
        font-size: 16px;
    }

    .main-content {
        padding: 32px;
    }

    .content-container {
        max-width: 100%;
    }

    .page-header h1 {
        font-size: 28px;
    }

    .folder-title {
        font-size: 32px;
    }

    .overview-section {
        grid-template-columns: repeat(2, 1fr);
    }

    .home-grid {
        grid-template-columns: 1fr 1fr;
        gap: 20px;
    }

    .study-options-grid {
        grid-template-columns: repeat(4, 1fr);
    }

    .items-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .friends-grid {
        grid-template-columns: repeat(3, 1fr);
    }

    .cards-grid,
    .practice-options,
    .games-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .friend-card-avatar {
        width: 60px;
        height: 60px;
        font-size: 24px;
    }

    .auth-container {
        max-width: 420px;
    }

    .profile-grid {
        grid-template-columns: 1fr;
    }
}

@media (min-width: 769px) {
    .study-options-grid {
        grid-template-columns: repeat(4, 1fr);
    }
}

@media (max-width: 900px) {
    .games-body {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    .mobile-menu-toggle {
        display: block;
    }

    .mobile-sidebar {
        display: block;
    }

    .main-content {
        padding-top: 70px;
        overflow-x: hidden;
        width: 100%;
    }

    .content-container {
        width: 100%;
        box-sizing: border-box;
    }

    .page-header {
        padding-top: 0;
        flex-direction: row;
        flex-wrap: wrap;
    }

    .page-header h1 {
        font-size: 28px;
    }

    .study-options-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .overview-section {
        grid-template-columns: repeat(2, 1fr);
    }

    .home-grid {
        grid-template-columns: 1fr;
    }

    .items-grid,
    .friends-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .cards-grid,
    .practice-options,
    .games-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .auth-container {
        max-width: 480px;
    }

    .auth-box {
        padding: 40px 32px;
    }

    .mobile-sidebar .nav {
        display: flex;
        flex-direction: column;
        padding: 20px 12px;
    }

    .mobile-sidebar .nav-item {
        flex-direction: row;
        text-align: left;
        justify-content: flex-start;
        padding: 12px 16px;
    }

    .mobile-sidebar .nav-icon {
        font-size: 18px;
    }

    .mobile-sidebar .nav-divider {
        display: block;
    }

    .mobile-sidebar .nav-section-header {
        display: block;
    }

    .mobile-sidebar .folder-item,
    .mobile-sidebar .new-folder-btn {
        display: flex;
    }

    .mobile-sidebar .sidebar-footer {
        display: block;
        position: static;
        margin-top: 8px;
    }
}

@media (min-width: 481px) and (max-width: 768px) {
    .sidebar {
        display: none;
    }

    .main-content {
        padding: 24px;
        padding-top: 70px;
    }
}

@media (max-width: 500px) {
    .games-2x2 {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .sidebar {
        display: none;
    }

    .main-content {
        padding: 16px;
        padding-top: 70px;
        overflow-x: hidden;
        width: 100%;
    }

    .content-container {
        padding: 0;
        width: 100%;
        box-sizing: border-box;
    }

    .main-layout {
        flex-direction: column;
    }

    .page-header {
        flex-direction: column;
        gap: 16px;
        align-items: flex-start;
    }

    .page-header h1 {
        font-size: 24px;
    }

    .folder-title {
        font-size: 28px;
    }

    .create-btn {
        width: 100%;
        justify-content: center;
    }

    .study-options-grid {
        grid-template-columns: 1fr;
        gap: 12px;
        width: 100%;
    }

    .study-option-card {
        padding: 16px;
        width: 100%;
        box-sizing: border-box;
    }

    .overview-section {
        grid-template-columns: 1fr;
        gap: 12px;
    }

    .overview-card {
        padding: 16px;
    }

    .home-grid {
        grid-template-columns: 1fr;
    }

    .section-card {
        padding: 16px;
    }

    .continue-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
    }

    .continue-icon {
        font-size: 32px;
    }

    .progress-bar {
        width: 100%;
    }

    .friend-avatar {
        width: 32px;
        height: 32px;
        font-size: 14px;
    }

    .friend-name {
        font-size: 13px;
    }

    .friend-score {
        font-size: 12px;
    }

    .items-grid,
    .recent-items-grid,
    .friends-grid {
        grid-template-columns: 1fr;
        gap: 16px;
    }

    .cards-grid,
    .practice-options,
    .games-grid {
        grid-template-columns: 1fr;
    }

    .auth-container {
        max-width: 100%;
    }

    .auth-box {
        padding: 32px 24px;
    }

    .breadcrumb {
        font-size: 12px;
        flex-wrap: wrap;
    }

    .stats-grid {
        grid-template-columns: 1fr;
    }

    .folder-contents {
        padding: 20px;
    }

    .timeline-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 8px;
    }

    .timeline-badge {
        align-self: flex-start;
    }

    .goal-circle {
        width: 90px;
        height: 90px;
    }

    .goal-svg {
        width: 90px;
        height: 90px;
    }

    .goal-percentage {
        font-size: 18px;
    }

    .achievement-icon {
        font-size: 24px;
    }

    .friend-card-avatar {
        width: 60px;
        height: 60px;
        font-size: 24px;
    }

    .flashcard {
        padding: 40px 20px;
        min-height: 250px;
    }

    .flashcard-content {
        font-size: 18px;
    }

    .flashcard-controls {
        flex-direction: column;
        width: 100%;
    }

    .nav-btn,
    .flip-btn {
        width: 100%;
    }

    .question-card {
        padding: 16px;
    }

    .social-buttons {
        grid-template-columns: 1fr;
    }

    .section-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 16px;
    }

    .section-header h2 {
        font-size: 20px;
    }

    .user-profile-section {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
    }

    .user-profile-section .friend-avatar {
        width: 48px;
        height: 48px;
        font-size: 20px;
    }

    .user-profile-section h1 {
        font-size: 24px;
    }

    .header-row {
        flex-direction: column;
        align-items: flex-start;
        gap: 6px;
    }

    .avatar-picker {
        grid-template-columns: repeat(4, 1fr);
        gap: 8px;
    }

    .avatar-img {
        width: 48px;
        height: 48px;
    }

    .avatar-picker-scrollable {
        grid-template-columns: repeat(4, 1fr);
        gap: 8px;
        max-height: 300px;
    }

    .summary-section {
        padding: 20px;
        margin-top: 32px;
    }

    .add-summary-btn {
        padding: 16px;
        font-size: 13px;
    }

    .summary-textarea {
        font-size: 14px;
        padding: 12px;
    }

    .summary-actions {
        flex-direction: column;
    }

    .summary-save-btn,
    .summary-cancel-btn {
        width: 100%;
    }

    .summary-edit-btn {
        position: static;
        width: 100%;
        margin-top: 12px;
    }

    .modal-box {
        width: 95%;
        margin: 20px;
    }

    .modal-header {
        padding: 20px 20px 16px;
    }

    .modal-header h3 {
        font-size: 18px;
    }

    .modal-body {
        padding: 20px;
    }

    .modal-footer {
        flex-direction: column;
        padding: 16px 20px 20px;
    }

    .modal-btn {
        width: 100%;
    }

    .profile-header-card {
        flex-direction: column;
        text-align: center;
    }

    .profile-avatar-large {
        width: 80px;
        height: 80px;
        font-size: 32px;
    }

    .setting-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
    }

    .secondary-btn,
    .danger-btn {
        width: 100%;
    }
}

@media (max-width: 360px) {
    body {
        font-size: 14px;
    }

    .page-header h1 {
        font-size: 20px;
    }

    .folder-title {
        font-size: 24px;
    }

    .section-card-header h2,
    .content-container > h2 {
        font-size: 16px;
    }

    .overview-value {
        font-size: 20px;
    }

    .overview-label {
        font-size: 11px;
    }

    .create-btn,
    .study-btn {
        font-size: 13px;
        padding: 10px;
    }

    .streak-number {
        font-size: 14px;
    }

    .streak-text {
        font-size: 12px;
    }
}

@media (max-width: 600px) {
    .user-profile-section {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
    }

    .user-profile-section .friend-avatar {
        width: 48px;
        height: 48px;
        font-size: 20px;
    }

    .user-profile-section h1 {
        font-size: 24px;
    }
}

@media (max-height: 500px) and (orientation: landscape) {
    .sidebar {
        display: none;
    }

    .main-content {
        padding: 16px;
    }

    .overview-section {
        grid-template-columns: repeat(4, 1fr);
        gap: 12px;
    }

    .overview-card {
        padding: 12px;
    }

    .overview-value {
        font-size: 20px;
    }

    .overview-label {
        font-size: 11px;
    }

    .home-grid {
        grid-template-columns: 1fr 1fr;
        gap: 16px;
    }

    .section-card {
        padding: 16px;
    }
}

@media (hover: none) and (pointer: coarse) {
    .nav-item,
    .study-btn,
    .create-btn,
    .continue-btn,
    .message-btn,
    .play-btn,
    .start-btn {
        min-height: 44px;
    }

    .nav-item {
        padding: 12px 16px;
    }

    .nav-item:hover,
    .feature-card:hover,
    .study-option-card:hover,
    .item-card:hover,
    .game-card:hover,
    .lib2-card:hover {
        transform: none;
    }

    .nav-item:active,
    .feature-card:active,
    .study-option-card:active {
        opacity: 0.8;
    }

    .flashcard {
        padding: 60px 30px;
    }
}

@media print {
    .sidebar,
    .sidebar-footer,
    .create-btn,
    .logout-btn,
    .nav,
    .breadcrumb {
        display: none;
    }

    .main-content {
        margin: 0;
        padding: 0;
    }

    .section-card {
        page-break-inside: avoid;
    }
}

@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
    body {
        -webkit-font-smoothing: antialiased;
        -moz-osx-font-smoothing: grayscale;
    }
}

@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}