:root {
    --coursera-navy: #0a1e3c;
    --coursera-blue: #2a73ff;
    --coursera-light-bg: #f9fafc;
    --coursera-border: #e6e8ec;
    --coursera-gray: #6b6f76;
    --coursera-card-shadow: 0 8px 20px rgba(0, 0, 0, 0.02), 0 4px 12px rgba(0, 20, 40, 0.04);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: system-ui, -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', 'Inter', sans-serif;
}

body {
    background-color: #ffffff;
    color: #1f1f1f;
    line-height: 1.5;
}

a {
    text-decoration: none;
    color: inherit;
}

.container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 32px;
}

.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px 0;
    border-bottom: 1px solid var(--coursera-border);
    background-color: white;
    flex-wrap: wrap;
}

.logo {
    font-size: 1.6rem;
    font-weight: 700;
    letter-spacing: -0.3px;
    color: var(--coursera-navy);
}

.logo span {
    color: var(--coursera-blue);
}

.nav-links {
    display: flex;
    gap: 32px;
    font-weight: 500;
    color: #2a3a4a;
}

.nav-links a {
    text-decoration: none;
    color: inherit;
    font-size: 0.95rem;
}

.nav-links a:hover {
    color: var(--coursera-blue);
}

.nav-links a.active {
    color: var(--coursera-blue);
    font-weight: 600;
    position: relative;
}

.nav-links a.active::after {
    content: '';
    position: absolute;
    bottom: -4px;
    left: 0;
    right: 0;
    height: 2px;
    background: var(--coursera-blue);
    border-radius: 1px;
}

.nav-actions {
    display: flex;
    gap: 16px;
    align-items: center;
}

.nav-actions .login {
    background: none;
    border: none;
    font-weight: 600;
    color: var(--coursera-navy);
    cursor: pointer;
    padding: 8px 16px;
    font-size: 0.95rem;
}

.nav-actions .signup {
    background-color: var(--coursera-navy);
    color: white;
    border: none;
    padding: 8px 18px;
    border-radius: 30px;
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    transition: background 0.2s;
}

.nav-actions .signup:hover {
    background-color: #14325c;
}

.nav-actions .user-info {
    display: flex;
    align-items: center;
    gap: 10px;
}

.nav-actions .user-info .user-name {
    font-weight: 600;
    color: var(--coursera-navy);
    font-size: 0.95rem;
}

.nav-actions .user-info .user-email {
    color: #666;
    font-size: 0.85rem;
    padding-right: 8px;
    border-right: 1px solid #ddd;
}

.nav-actions .user-info .member-badge {
    background: linear-gradient(135deg, #ffd700, #ff8c00);
    color: white;
    padding: 3px 10px;
    border-radius: 12px;
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.5px;
}

.nav-actions .user-info .member-expired {
    background: #e0e0e0;
    color: #888;
}

.nav-actions .logout {
    background: none;
    border: none;
    font-weight: 600;
    color: #666;
    cursor: pointer;
    padding: 8px 16px;
    font-size: 0.9rem;
    transition: color 0.2s;
}

.nav-actions .logout:hover {
    color: var(--coursera-navy);
}

.mobile-menu-icon {
    display: none;
    font-size: 1.8rem;
    cursor: pointer;
    color: var(--coursera-navy);
}

.section-title {
    font-size: 2.2rem;
    font-weight: 600;
    color: var(--coursera-navy);
    margin-bottom: 24px;
    letter-spacing: -0.02em;
}

.footer {
    padding: 40px 0 60px;
    color: #5e6873;
    border-top: 1px solid var(--coursera-border);
    font-size: 0.9rem;
}

.footer small {
    display: block;
    margin-top: 24px;
    color: #7b8799;
}

.page-container {
    min-height: calc(100vh - 200px);
    padding: 40px 0;
}

.page-card {
    background: white;
    border-radius: 24px;
    padding: 40px;
    box-shadow: var(--coursera-card-shadow);
    border: 1px solid var(--coursera-border);
}

.page-title {
    font-size: 2rem;
    font-weight: 600;
    color: var(--coursera-navy);
    margin-bottom: 16px;
}

.page-intro {
    font-size: 1.1rem;
    color: var(--coursera-gray);
    margin-bottom: 32px;
}

.page-content {
    color: #374151;
    line-height: 1.8;
}

.page-content h2 {
    font-size: 1.4rem;
    font-weight: 600;
    color: var(--coursera-navy);
    margin: 24px 0 12px;
}

.page-content p {
    margin-bottom: 16px;
}

.page-content ul {
    margin-left: 24px;
    margin-bottom: 16px;
}

.page-content li {
    margin-bottom: 8px;
}

.feature-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
    margin-top: 32px;
}

.feature-item {
    text-align: center;
    padding: 32px 20px;
    background: var(--coursera-light-bg);
    border-radius: 20px;
    transition: transform 0.2s;
}

.feature-item:hover {
    transform: translateY(-4px);
}

.feature-icon {
    font-size: 3rem;
    margin-bottom: 16px;
}

.feature-title {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--coursera-navy);
    margin-bottom: 8px;
}

.feature-item p {
    color: var(--coursera-gray);
    font-size: 0.95rem;
}

.auth-page {
    min-height: calc(100vh - 200px);
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 40px 20px;
    background: linear-gradient(145deg, #ffffff 0%, #f8faff 100%);
}

.auth-container {
    width: 100%;
    max-width: 420px;
    background: white;
    border-radius: 24px;
    padding: 40px;
    box-shadow: var(--coursera-card-shadow);
    border: 1px solid var(--coursera-border);
}

.auth-title {
    font-size: 1.8rem;
    font-weight: 600;
    color: var(--coursera-navy);
    margin-bottom: 24px;
    text-align: center;
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    font-weight: 500;
    color: var(--coursera-navy);
    margin-bottom: 8px;
    font-size: 0.95rem;
}

.form-group input {
    width: 100%;
    padding: 12px 16px;
    border: 1px solid var(--coursera-border);
    border-radius: 12px;
    font-size: 1rem;
    transition: all 0.2s;
    outline: none;
    box-sizing: border-box;
}

.form-group input:focus {
    border-color: var(--coursera-blue);
    box-shadow: 0 0 0 3px rgba(42, 115, 255, 0.1);
}

.form-group-captcha {
    display: flex;
    align-items: center;
    gap: 12px;
}

.form-group-captcha input {
    flex: 1;
}

.captcha-img {
    height: 44px;
    cursor: pointer;
    border-radius: 8px;
    border: 1px solid var(--coursera-border);
}

.email-code-group {
    display: flex;
    gap: 12px;
}

.email-code-group input {
    flex: 1;
}

.btn-code {
    padding: 12px 20px;
    background: var(--coursera-navy);
    color: white;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    white-space: nowrap;
    font-weight: 500;
    transition: background 0.2s;
}

.btn-code:hover {
    background: #14325c;
}

.btn-code:disabled {
    background: #ccc;
    cursor: not-allowed;
}

.btn-submit {
    width: 100%;
    padding: 14px;
    background: var(--coursera-navy);
    color: white;
    border: none;
    border-radius: 30px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s;
    margin-top: 8px;
}

.btn-submit:hover {
    background: #14325c;
}

.auth-footer {
    text-align: center;
    margin-top: 24px;
    color: var(--coursera-gray);
    font-size: 0.95rem;
}

.auth-footer a {
    color: var(--coursera-blue);
    text-decoration: none;
    font-weight: 500;
}

.auth-footer a:hover {
    text-decoration: underline;
}

.error-msg {
    background: #fee2e2;
    color: #dc2626;
    padding: 12px 16px;
    border-radius: 12px;
    margin-bottom: 20px;
    font-size: 0.95rem;
}

.success-msg {
    background: #dcfce7;
    color: #16a34a;
    padding: 12px 16px;
    border-radius: 12px;
    margin-bottom: 20px;
    font-size: 0.95rem;
}

@media (max-width: 900px) {
    .nav-links, .nav-actions .login { display: none; }
    .mobile-menu-icon { display: block; }
    .feature-grid { grid-template-columns: 1fr; }
}

@media (max-width: 600px) {
    .container { padding: 0 20px; }
    .page-card { padding: 24px; }
    .feature-grid { grid-template-columns: 1fr; }
}

.modal-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.6);
    z-index: 9999;
    justify-content: center;
    align-items: center;
}
.modal-overlay.active {
    display: flex;
}
.modal-content {
    background: white;
    border-radius: 16px;
    padding: 32px;
    max-width: 500px;
    width: 90%;
    text-align: center;
    position: relative;
    animation: modalSlideIn 0.3s ease;
}
@keyframes modalSlideIn {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}
.modal-close {
    position: absolute;
    top: 16px;
    right: 16px;
    background: none;
    border: none;
    font-size: 24px;
    cursor: pointer;
    color: #999;
}
.modal-close:hover {
    color: #333;
}
.modal-title {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--coursera-navy);
    margin-bottom: 16px;
}