* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #c75050;
    --primary-dark: #a84444;
    --secondary-color: #e6b44c;
    --background: #f5f5f5;
    --card-bg: #f8f9fa;
    --text-primary: #1a1a1a;
    --text-secondary: #757575;
    --success: #6db070;
    --error: #d96a6a;
    --border-radius: 12px;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.15);
}

body {
    font-family: 'Lato', sans-serif;
    background: #1a1a1a;
    min-height: 100vh;
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-tap-highlight-color: transparent;
}

.container {
    max-width: 960px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

header {
    text-align: center;
    padding: 30px 0;
    color: white;
}

header h1 {
    font-size: 2.2rem;
    margin-bottom: 8px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

.subtitle {
    color: rgba(255, 255, 255, 0.8);
    font-size: 1.1rem;
}

main {
    flex: 1;
    display: flex;
    gap: 20px;
    align-items: flex-start;
}

#grammar-menu {
    width: 220px;
    flex-shrink: 0;
    display: flex;
    flex-direction: column;
    gap: 8px;
    position: sticky;
    top: 20px;
}

.menu-btn {
    display: block;
    width: 100%;
    padding: 12px 16px;
    border: 2px solid #e0e0e0;
    border-radius: var(--border-radius);
    background: var(--card-bg);
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    font-family: 'Lato', sans-serif;
    cursor: pointer;
    transition: all 0.3s ease;
    text-align: left;
}

.menu-btn:hover {
    border-color: var(--primary-color);
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.menu-btn.active {
    border-color: var(--primary-color);
    background: var(--primary-color);
    color: white;
}

.menu-error {
    color: var(--error);
    font-style: italic;
}

#grammar-content {
    flex: 1;
    background: var(--card-bg);
    border-radius: var(--border-radius);
    padding: 30px;
    box-shadow: var(--shadow-lg);
    min-height: 400px;
}

.grammar-welcome {
    text-align: center;
    padding: 40px 0;
}

.grammar-welcome h2 {
    color: var(--text-primary);
    margin-bottom: 10px;
    font-size: 1.5rem;
}

.grammar-welcome p {
    color: var(--text-secondary);
}

#grammar-content h1 {
    font-size: 1.8rem;
    color: var(--primary-color);
    margin-bottom: 20px;
    padding-bottom: 10px;
    border-bottom: 2px solid #e0e0e0;
}

#grammar-content h2 {
    font-size: 1.4rem;
    color: var(--text-primary);
    margin-top: 30px;
    margin-bottom: 12px;
}

#grammar-content h3 {
    font-size: 1.15rem;
    color: var(--text-primary);
    margin-top: 24px;
    margin-bottom: 10px;
}

#grammar-content h4,
#grammar-content h5,
#grammar-content h6 {
    color: var(--text-primary);
    margin-top: 20px;
    margin-bottom: 8px;
}

#grammar-content p {
    margin-bottom: 14px;
    line-height: 1.7;
}

#grammar-content ul,
#grammar-content ol {
    margin-bottom: 14px;
    padding-left: 24px;
}

#grammar-content li {
    margin-bottom: 6px;
    line-height: 1.6;
}

#grammar-content strong {
    color: var(--primary-dark);
}

#grammar-content em {
    color: var(--text-secondary);
}

#grammar-content table {
    width: 100%;
    border-collapse: collapse;
    margin: 16px 0 20px;
    font-size: 0.95rem;
}

#grammar-content thead {
    background: var(--primary-color);
    color: white;
}

#grammar-content th {
    padding: 10px 14px;
    text-align: left;
    font-weight: 600;
}

#grammar-content th:first-child {
    border-radius: 8px 0 0 0;
}

#grammar-content th:last-child {
    border-radius: 0 8px 0 0;
}

#grammar-content td {
    padding: 10px 14px;
    border-bottom: 1px solid #e0e0e0;
}

#grammar-content tbody tr:nth-child(even) {
    background: rgba(0, 0, 0, 0.03);
}

#grammar-content tbody tr:hover {
    background: rgba(199, 80, 80, 0.06);
}

#grammar-content tbody tr:last-child td:first-child {
    border-radius: 0 0 0 8px;
}

#grammar-content tbody tr:last-child td:last-child {
    border-radius: 0 0 8px 0;
}

#grammar-content code {
    background: rgba(0, 0, 0, 0.06);
    padding: 2px 6px;
    border-radius: 4px;
    font-size: 0.9em;
    font-family: 'Courier New', monospace;
}

#grammar-content pre {
    background: #2d2d2d;
    color: #f8f8f2;
    padding: 16px;
    border-radius: 8px;
    overflow-x: auto;
    margin-bottom: 16px;
}

#grammar-content pre code {
    background: none;
    padding: 0;
    color: inherit;
}

#grammar-content blockquote {
    border-left: 4px solid var(--secondary-color);
    padding: 10px 16px;
    margin: 16px 0;
    background: rgba(230, 180, 76, 0.08);
    border-radius: 0 8px 8px 0;
    color: var(--text-secondary);
}

#grammar-content hr {
    border: none;
    border-top: 2px solid #e0e0e0;
    margin: 24px 0;
}

footer {
    text-align: center;
    padding: 20px 0;
    color: rgba(255, 255, 255, 0.6);
    font-size: 0.9rem;
    margin-top: 20px;
}

footer .footer-content {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 12px;
}

footer .copyright {
    font-size: 0.8rem;
    margin: 0;
    color: rgba(255, 255, 255, 0.4);
}

footer .github-link {
    display: inline-flex;
    align-items: center;
}

footer .github-link img {
    height: 20px;
    width: 20px;
    opacity: 0.6;
    filter: brightness(1.2);
}

footer .github-link:hover img {
    opacity: 1;
}

@media (max-width: 768px) {
    main {
        flex-direction: column;
    }

    #grammar-menu {
        width: 100%;
        position: static;
        flex-direction: row;
        flex-wrap: wrap;
        gap: 8px;
    }

    .menu-btn {
        width: auto;
        flex: 1 1 auto;
        text-align: center;
    }

    #grammar-content {
        padding: 20px;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 12px;
    }

    header h1 {
        font-size: 1.8rem;
    }

    #grammar-content {
        padding: 16px;
    }

    #grammar-content h1 {
        font-size: 1.5rem;
    }

    #grammar-content h2 {
        font-size: 1.2rem;
    }
}