/* ============================================
   MIT Sloan Management Review - Styles
   Modern, responsive design inspired by MIT
   ============================================ */

/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    /* MIT Sloan Review Colors (actual site) */
    --color-primary: #005b9c;  /* MIT Sloan Blue */
    --color-primary-dark: #004875;
    --color-secondary: #00e0ff;  /* Cyan accent */
    --color-accent: #ed1b2e;  /* Red accent */
    --color-mit-red: #A31F34;  /* MIT Red (secondary) */

    /* Grayscale */
    --color-black: #1A1A1A;
    --color-gray-900: #2D2D2D;
    --color-gray-800: #404040;
    --color-gray-700: #5C5C5C;
    --color-gray-600: #757575;
    --color-gray-500: #9E9E9E;
    --color-gray-400: #BDBDBD;
    --color-gray-300: #E0E0E0;
    --color-gray-200: #EEEEEE;
    --color-gray-100: #F5F5F5;
    --color-white: #FFFFFF;

    /* Semantic Colors */
    --color-success: #4CAF50;
    --color-warning: #FF9800;
    --color-error: #F44336;
    --color-info: #2196F3;

    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-weight-light: 300;
    --font-weight-regular: 400;
    --font-weight-medium: 500;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;
    --font-weight-extrabold: 800;

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-2xl: 4rem;
    --spacing-3xl: 6rem;

    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    --radius-full: 9999px;

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 350ms ease;

    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.15);
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    font-size: 1.125rem;  /* 18px - matches MIT Sloan */
    line-height: 1.6;
    color: var(--color-gray-900);
    background-color: var(--color-white);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    padding-top: 92px;  /* Account for fixed header */
}

/* Container */
.container {
    max-width: 1500px;  /* Matches MIT Sloan */
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

@media (min-width: 768px) {
    .container {
        padding: 0 var(--spacing-lg);
    }
}

/* Header & Navigation */
.header {
    position: fixed;  /* Fixed header like MIT Sloan */
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    height: 92px;  /* Matches MIT Sloan header height */
    background-color: var(--color-white);
    border-bottom: 1px solid var(--color-gray-300);
    box-shadow: var(--shadow-sm);
    display: flex;
    align-items: center;
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md) 0;
    gap: var(--spacing-lg);
}

.nav-brand {}

.logo {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    line-height: 1.2;
    color: var(--color-black);
}

.logo span {
    font-size: 0.875rem;
    font-weight: var(--font-weight-medium);
    color: var(--color-gray-700);
}

.nav-menu {
    display: none;
    list-style: none;
    gap: var(--spacing-lg);
}

.nav-menu li a {
    text-decoration: none;
    color: var(--color-gray-800);
    font-weight: var(--font-weight-medium);
    transition: color var(--transition-fast);
}

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

.nav-toggle {
    display: flex;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
}

.nav-toggle span {
    width: 24px;
    height: 2px;
    background-color: var(--color-gray-900);
    transition: all var(--transition-base);
}

.nav-toggle.active span:nth-child(1) {
    transform: rotate(45deg) translate(6px, 6px);
}

.nav-toggle.active span:nth-child(2) {
    opacity: 0;
}

.nav-toggle.active span:nth-child(3) {
    transform: rotate(-45deg) translate(6px, -6px);
}

@media (min-width: 768px) {
    .nav-menu {
        display: flex;
    }

    .nav-toggle {
        display: none;
    }
}

/* Mobile Menu */
.nav-menu.active {
    display: flex;
    flex-direction: column;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background-color: var(--color-white);
    border-bottom: 1px solid var(--color-gray-300);
    padding: var(--spacing-md);
    box-shadow: var(--shadow-lg);
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    font-weight: var(--font-weight-semibold);
    text-align: center;
    text-decoration: none;
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
    cursor: pointer;
    border: none;
    font-size: 0.9375rem;
}

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

.btn-primary:hover {
    background-color: var(--color-primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-large {
    padding: 1rem 2rem;
    font-size: 1.0625rem;
}

/* Hero Section */
.hero {
    padding: var(--spacing-3xl) 0;
    background: linear-gradient(135deg, var(--color-gray-100) 0%, var(--color-white) 100%);
}

.hero .container {
    display: grid;
    gap: var(--spacing-xl);
    align-items: center;
}

@media (min-width: 1024px) {
    .hero .container {
        grid-template-columns: 1fr 1fr;
    }
}

.hero-content {}

.hero-badge {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: var(--color-primary);
    color: var(--color-white);
    font-size: 0.875rem;
    font-weight: var(--font-weight-semibold);
    border-radius: var(--radius-full);
    margin-bottom: var(--spacing-md);
}

.hero-title {
    font-size: 2.5rem;
    font-weight: var(--font-weight-extrabold);
    line-height: 1.2;
    color: var(--color-black);
    margin-bottom: var(--spacing-md);
}

@media (min-width: 768px) {
    .hero-title {
        font-size: 3rem;
    }
}

.hero-excerpt {
    font-size: 1.125rem;
    color: var(--color-gray-700);
    margin-bottom: var(--spacing-lg);
    line-height: 1.7;
}

.hero-meta {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-xl);
    padding: var(--spacing-md) 0;
    border-top: 1px solid var(--color-gray-300);
    border-bottom: 1px solid var(--color-gray-300);
}

@media (min-width: 640px) {
    .hero-meta {
        flex-direction: row;
        justify-content: space-between;
        align-items: center;
    }
}

.author-info {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.author-avatar {
    width: 48px;
    height: 48px;
    border-radius: var(--radius-full);
}

.author-name {
    display: block;
    font-weight: var(--font-weight-semibold);
    color: var(--color-black);
}

.author-title {
    display: block;
    font-size: 0.875rem;
    color: var(--color-gray-600);
}

.article-info {
    display: flex;
    gap: var(--spacing-sm);
    font-size: 0.9375rem;
    color: var(--color-gray-600);
}

.separator {
    color: var(--color-gray-400);
}

.hero-image {
    border-radius: var(--radius-xl);
    overflow: hidden;
    box-shadow: var(--shadow-xl);
}

.hero-image img {
    width: 100%;
    height: auto;
    display: block;
}

/* Sections */
.articles-section,
.topics-section,
.newsletter-section {
    padding: var(--spacing-3xl) 0;
}

.section-header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
}

.section-title {
    font-size: 2.5rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-black);
    margin-bottom: var(--spacing-sm);
}

.section-subtitle {
    font-size: 1.125rem;
    color: var(--color-gray-600);
}

/* Articles Grid */
.articles-grid {
    display: grid;
    gap: var(--spacing-xl);
    grid-template-columns: 1fr;
}

@media (min-width: 640px) {
    .articles-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 1024px) {
    .articles-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}

/* Article Cards */
.article-card {
    background-color: var(--color-white);
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
    cursor: pointer;
}

.article-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-xl);
}

.article-image {
    position: relative;
    width: 100%;
    height: 200px;
    overflow: hidden;
}

.article-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform var(--transition-slow);
}

.article-card:hover .article-image img {
    transform: scale(1.05);
}

.category-badge {
    position: absolute;
    top: var(--spacing-sm);
    left: var(--spacing-sm);
    padding: 0.375rem 0.75rem;
    background-color: var(--color-primary);
    color: var(--color-white);
    font-size: 0.75rem;
    font-weight: var(--font-weight-semibold);
    border-radius: var(--radius-md);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.category-leadership {
    background-color: #2196F3;
}

.category-sustainability {
    background-color: #4CAF50;
}

.category-innovation {
    background-color: #9C27B0;
}

.category-finance {
    background-color: #FF9800;
}

.category-strategy {
    background-color: #607D8B;
}

.article-content {
    padding: var(--spacing-md);
}

.article-title {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-black);
    margin-bottom: var(--spacing-sm);
    line-height: 1.3;
}

.article-excerpt {
    font-size: 0.9375rem;
    color: var(--color-gray-700);
    line-height: 1.6;
    margin-bottom: var(--spacing-md);
}

.article-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: var(--spacing-sm);
    border-top: 1px solid var(--color-gray-200);
}

.author-small {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.author-small img {
    width: 32px;
    height: 32px;
    border-radius: var(--radius-full);
}

.author-small span {
    font-size: 0.875rem;
    font-weight: var(--font-weight-medium);
    color: var(--color-gray-800);
}

.read-time {
    font-size: 0.875rem;
    color: var(--color-gray-600);
}

/* Topics Section */
.topics-section {
    background-color: var(--color-gray-100);
}

.topics-grid {
    display: grid;
    gap: var(--spacing-lg);
    grid-template-columns: 1fr;
}

@media (min-width: 640px) {
    .topics-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 1024px) {
    .topics-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}

.topic-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    padding: var(--spacing-xl);
    background-color: var(--color-white);
    border-radius: var(--radius-lg);
    text-decoration: none;
    transition: all var(--transition-base);
    box-shadow: var(--shadow-sm);
}

.topic-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.topic-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.topic-card h3 {
    font-size: 1.5rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-black);
    margin-bottom: var(--spacing-xs);
}

.topic-card p {
    font-size: 0.9375rem;
    color: var(--color-gray-700);
    margin-bottom: var(--spacing-sm);
}

.topic-count {
    font-size: 0.875rem;
    color: var(--color-gray-600);
}

/* Newsletter Section */
.newsletter-section {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
    color: var(--color-white);
}

.newsletter-content {
    text-align: center;
    max-width: 640px;
    margin: 0 auto;
}

.newsletter-text h2 {
    font-size: 2rem;
    font-weight: var(--font-weight-bold);
    margin-bottom: var(--spacing-sm);
}

.newsletter-text p {
    font-size: 1.125rem;
    margin-bottom: var(--spacing-xl);
    opacity: 0.95;
}

.newsletter-form {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
}

@media (min-width: 640px) {
    .newsletter-form {
        flex-direction: row;
    }
}

.newsletter-input {
    flex: 1;
    padding: 1rem 1.5rem;
    border: none;
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-family: var(--font-family);
}

.newsletter-input::placeholder {
    color: var(--color-gray-500);
}

.newsletter-input:focus {
    outline: 2px solid var(--color-white);
    outline-offset: 2px;
}

.newsletter-form .btn {
    white-space: nowrap;
}

.newsletter-form .btn-primary {
    background-color: var(--color-white);
    color: var(--color-primary);
}

.newsletter-form .btn-primary:hover {
    background-color: var(--color-gray-100);
}

.newsletter-privacy {
    font-size: 0.875rem;
    opacity: 0.85;
}

.newsletter-privacy a {
    color: var(--color-white);
    text-decoration: underline;
}

/* Footer */
.footer {
    background-color: var(--color-gray-900);
    color: var(--color-gray-400);
    padding: var(--spacing-3xl) 0 var(--spacing-lg);
}

.footer-grid {
    display: grid;
    gap: var(--spacing-xl);
    grid-template-columns: 1fr;
    margin-bottom: var(--spacing-xl);
}

@media (min-width: 640px) {
    .footer-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 1024px) {
    .footer-grid {
        grid-template-columns: 2fr 1fr 1fr 1fr;
    }
}

.footer-column h4,
.footer-column h5 {
    color: var(--color-white);
    font-weight: var(--font-weight-semibold);
    margin-bottom: var(--spacing-md);
}

.footer-column p {
    margin-bottom: var(--spacing-md);
    line-height: 1.6;
}

.footer-column ul {
    list-style: none;
}

.footer-column ul li {
    margin-bottom: var(--spacing-sm);
}

.footer-column ul li a {
    color: var(--color-gray-400);
    text-decoration: none;
    transition: color var(--transition-fast);
}

.footer-column ul li a:hover {
    color: var(--color-white);
}

.social-links {
    display: flex;
    gap: var(--spacing-md);
}

.social-links a {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    background-color: var(--color-gray-800);
    border-radius: var(--radius-md);
    color: var(--color-gray-400);
    transition: all var(--transition-base);
}

.social-links a:hover {
    background-color: var(--color-primary);
    color: var(--color-white);
    transform: translateY(-2px);
}

.footer-bottom {
    text-align: center;
    padding-top: var(--spacing-lg);
    border-top: 1px solid var(--color-gray-800);
    font-size: 0.875rem;
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeIn 0.6s ease-out;
}

/* Success Message */
.success-message {
    position: fixed;
    bottom: var(--spacing-lg);
    right: var(--spacing-lg);
    padding: var(--spacing-md) var(--spacing-lg);
    background-color: var(--color-success);
    color: var(--color-white);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-xl);
    z-index: 10000;
    animation: fadeIn 0.3s ease;
}

/* Print Styles */
@media print {
    .header,
    .newsletter-section,
    .footer {
        display: none;
    }
}