/*
 * StartupBook.org - Main Stylesheet
 * High-performance, mobile-first design system
 * Optimized for Core Web Vitals and SEO
 */

/* ===========================
   CSS CUSTOM PROPERTIES (Design Tokens)
   =========================== */
:root {
    /* Color Palette */
    --color-primary: #6366F1;           /* Electric Indigo */
    --color-primary-dark: #4F46E5;
    --color-primary-light: #818CF8;
    --color-secondary: #8B5CF6;         /* Purple */
    --color-accent: #EC4899;            /* Pink accent */

    /* Neutrals */
    --color-text-primary: #111827;      /* Almost black */
    --color-text-secondary: #6B7280;    /* Gray */
    --color-text-tertiary: #9CA3AF;
    --color-background: #FFFFFF;
    --color-background-alt: #F9FAFB;
    --color-border: #E5E7EB;
    --color-border-light: #F3F4F6;

    /* Typography */
    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "Inter", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
    --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;

    /* Font Sizes - Fluid Typography */
    --text-xs: 0.75rem;      /* 12px */
    --text-sm: 0.875rem;     /* 14px */
    --text-base: 1rem;       /* 16px */
    --text-lg: 1.125rem;     /* 18px */
    --text-xl: 1.25rem;      /* 20px */
    --text-2xl: 1.5rem;      /* 24px */
    --text-3xl: 1.875rem;    /* 30px */
    --text-4xl: 2.25rem;     /* 36px */
    --text-5xl: 3rem;        /* 48px */

    /* Spacing Scale */
    --space-1: 0.25rem;      /* 4px */
    --space-2: 0.5rem;       /* 8px */
    --space-3: 0.75rem;      /* 12px */
    --space-4: 1rem;         /* 16px */
    --space-5: 1.25rem;      /* 20px */
    --space-6: 1.5rem;       /* 24px */
    --space-8: 2rem;         /* 32px */
    --space-10: 2.5rem;      /* 40px */
    --space-12: 3rem;        /* 48px */
    --space-16: 4rem;        /* 64px */
    --space-20: 5rem;        /* 80px */

    /* Layout */
    --container-width: 1200px;
    --container-padding: 1.5rem;
    --border-radius-sm: 0.375rem;  /* 6px */
    --border-radius-md: 0.5rem;    /* 8px */
    --border-radius-lg: 0.75rem;   /* 12px */

    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1);
    --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1);

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

    /* Z-index Scale */
    --z-header: 1000;
    --z-modal: 2000;
    --z-tooltip: 3000;
}

/* ===========================
   RESET & BASE STYLES
   =========================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    font-size: var(--text-base);
    line-height: 1.6;
    color: var(--color-text-primary);
    background-color: var(--color-background);
    overflow-x: hidden;
}

/* Improve performance for animations */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}

/* ===========================
   TYPOGRAPHY
   =========================== */
h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    color: var(--color-text-primary);
    margin-bottom: var(--space-4);
}

h1 { font-size: var(--text-4xl); }
h2 { font-size: var(--text-3xl); }
h3 { font-size: var(--text-2xl); }
h4 { font-size: var(--text-xl); }
h5 { font-size: var(--text-lg); }
h6 { font-size: var(--text-base); }

p {
    margin-bottom: var(--space-4);
}

a {
    color: var(--color-primary);
    text-decoration: none;
    transition: color var(--transition-fast);
}

a:hover {
    color: var(--color-primary-dark);
}

a:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
    border-radius: var(--border-radius-sm);
}

/* ===========================
   LAYOUT UTILITIES
   =========================== */
.container {
    width: 100%;
    max-width: var(--container-width);
    margin-left: auto;
    margin-right: auto;
    padding-left: var(--container-padding);
    padding-right: var(--container-padding);
}

/* ===========================
   HEADER & NAVIGATION
   =========================== */
.site-header {
    position: sticky;
    top: 0;
    background-color: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--color-border-light);
    z-index: var(--z-header);
    padding: var(--space-4) 0;
}

.nav-container {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    font-weight: 700;
    font-size: var(--text-lg);
    color: var(--color-text-primary);
    transition: opacity var(--transition-fast);
}

.logo:hover {
    opacity: 0.8;
}

.logo-text {
    font-weight: 700;
}

/* Mobile Menu Toggle */
.mobile-menu-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--space-2);
    color: var(--color-text-primary);
}

.mobile-menu-toggle:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
    border-radius: var(--border-radius-sm);
}

/* Navigation Menu */
.nav-menu {
    display: flex;
    align-items: center;
    gap: var(--space-6);
    list-style: none;
}

.nav-link {
    font-weight: 500;
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    transition: color var(--transition-fast);
    position: relative;
    padding: var(--space-2) 0;
}

.nav-link:hover,
.nav-link.active {
    color: var(--color-primary);
}

.nav-link.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 2px;
    background-color: var(--color-primary);
}

/* ===========================
   HERO SECTION
   =========================== */
.hero {
    padding: var(--space-20) 0;
    background: linear-gradient(135deg, #F9FAFB 0%, #FFFFFF 100%);
    border-bottom: 1px solid var(--color-border-light);
}

.hero-container {
    display: grid;
    gap: var(--space-12);
}

.hero-content {
    text-align: center;
    max-width: 800px;
    margin: 0 auto;
}

.hero-title {
    font-size: var(--text-4xl);
    font-weight: 800;
    line-height: 1.1;
    margin-bottom: var(--space-6);
    color: var(--color-text-primary);
}

.hero-description {
    font-size: var(--text-lg);
    color: var(--color-text-secondary);
    margin-bottom: var(--space-8);
    line-height: 1.7;
}

.hero-cta {
    display: flex;
    gap: var(--space-4);
    justify-content: center;
    flex-wrap: wrap;
}

/* ===========================
   BUTTONS
   =========================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--space-3) var(--space-6);
    font-size: var(--text-base);
    font-weight: 600;
    border-radius: var(--border-radius-md);
    border: none;
    cursor: pointer;
    transition: all var(--transition-fast);
    text-decoration: none;
    white-space: nowrap;
}

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

.btn-primary:hover {
    background-color: var(--color-primary-dark);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background-color: transparent;
    color: var(--color-primary);
    border: 2px solid var(--color-primary);
}

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

/* ===========================
   MAIN CONTENT SECTIONS
   =========================== */
.main-content {
    padding: var(--space-16) 0;
}

.section-header {
    text-align: center;
    margin-bottom: var(--space-12);
}

.section-title {
    font-size: var(--text-3xl);
    font-weight: 800;
    margin-bottom: var(--space-3);
}

.section-subtitle {
    font-size: var(--text-lg);
    color: var(--color-text-secondary);
}

.featured-section,
.latest-section,
.books-section {
    margin-bottom: var(--space-20);
}

/* ===========================
   ARTICLE CARDS (Featured)
   =========================== */
.articles-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: var(--space-8);
}

.article-card {
    background: white;
    border-radius: var(--border-radius-lg);
    overflow: hidden;
    border: 1px solid var(--color-border-light);
    transition: all var(--transition-base);
}

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

.card-link {
    display: block;
    color: inherit;
}

.card-link:hover {
    color: inherit;
}

.card-image-wrapper {
    position: relative;
    width: 100%;
    padding-top: 56.25%; /* 16:9 Aspect Ratio */
    background-color: var(--color-background-alt);
    overflow: hidden;
}

.card-image {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform var(--transition-slow);
}

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

.card-content {
    padding: var(--space-6);
}

.card-category {
    display: inline-block;
    font-size: var(--text-xs);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-primary);
    background-color: rgba(99, 102, 241, 0.1);
    padding: var(--space-1) var(--space-3);
    border-radius: var(--border-radius-sm);
    margin-bottom: var(--space-3);
}

.card-title {
    font-size: var(--text-xl);
    font-weight: 700;
    line-height: 1.3;
    margin-bottom: var(--space-3);
    color: var(--color-text-primary);
}

.card-excerpt {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin-bottom: var(--space-4);
}

.card-meta {
    display: flex;
    align-items: center;
    gap: var(--space-4);
    font-size: var(--text-xs);
    color: var(--color-text-tertiary);
}

.reading-time::before {
    content: '•';
    margin-right: var(--space-2);
}

/* ===========================
   GUIDES LIST
   =========================== */
.latest-section .section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    text-align: left;
    margin-bottom: var(--space-8);
}

.view-all-link {
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--color-primary);
    transition: transform var(--transition-fast);
}

.view-all-link:hover {
    transform: translateX(4px);
}

.guides-list {
    display: grid;
    gap: var(--space-6);
}

.guide-item {
    padding: var(--space-6);
    border: 1px solid var(--color-border-light);
    border-radius: var(--border-radius-lg);
    transition: all var(--transition-base);
}

.guide-item:hover {
    border-color: var(--color-primary);
    box-shadow: var(--shadow-md);
}

.guide-content {
    display: flex;
    flex-direction: column;
    gap: var(--space-3);
}

.guide-link {
    color: inherit;
}

.guide-category {
    display: inline-block;
    font-size: var(--text-xs);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-primary);
}

.guide-title {
    font-size: var(--text-lg);
    font-weight: 700;
    line-height: 1.4;
    color: var(--color-text-primary);
    transition: color var(--transition-fast);
}

.guide-link:hover .guide-title {
    color: var(--color-primary);
}

.guide-excerpt {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    line-height: 1.6;
}

.guide-meta {
    display: flex;
    align-items: center;
    gap: var(--space-4);
    font-size: var(--text-xs);
    color: var(--color-text-tertiary);
}

/* ===========================
   BOOKS SECTION
   =========================== */
.books-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: var(--space-8);
    justify-items: center;
}

.book-card {
    text-align: center;
    transition: transform var(--transition-base);
}

.book-card:hover {
    transform: translateY(-4px);
}

.book-cover-wrapper {
    margin-bottom: var(--space-4);
}

.book-cover-placeholder {
    box-shadow: var(--shadow-md);
    border-radius: var(--border-radius-sm);
    transition: box-shadow var(--transition-base);
}

.book-card:hover .book-cover-placeholder {
    box-shadow: var(--shadow-lg);
}

.book-title {
    font-size: var(--text-sm);
    font-weight: 600;
    margin-bottom: var(--space-2);
    color: var(--color-text-primary);
}

.book-author {
    font-size: var(--text-xs);
    color: var(--color-text-secondary);
}

/* ===========================
   AD PLACEHOLDERS (CLS Prevention)
   =========================== */
.ad-placeholder {
    background: linear-gradient(135deg, #F9FAFB 0%, #F3F4F6 100%);
    border: 1px dashed var(--color-border);
    border-radius: var(--border-radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 250px;
    margin: var(--space-8) 0;
}

.ad-placeholder::after {
    content: 'Advertisement';
    font-size: var(--text-xs);
    color: var(--color-text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.1em;
}

.ad-placeholder-horizontal {
    min-height: 90px;
}

#ad-slot-header {
    margin-top: var(--space-8);
}

/* ===========================
   FOOTER
   =========================== */
.site-footer {
    background-color: var(--color-background-alt);
    border-top: 1px solid var(--color-border-light);
    padding: var(--space-16) 0 var(--space-8);
    margin-top: var(--space-20);
}

.footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: var(--space-10);
    margin-bottom: var(--space-10);
}

.footer-heading {
    font-size: var(--text-xl);
    font-weight: 700;
    margin-bottom: var(--space-4);
}

.footer-description {
    color: var(--color-text-secondary);
    font-size: var(--text-sm);
    line-height: 1.6;
}

.footer-title {
    font-size: var(--text-sm);
    font-weight: 600;
    margin-bottom: var(--space-4);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.footer-links {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: var(--space-3);
}

.footer-links a {
    color: var(--color-text-secondary);
    font-size: var(--text-sm);
    transition: color var(--transition-fast);
}

.footer-links a:hover {
    color: var(--color-primary);
}

.newsletter-text {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    margin-bottom: var(--space-4);
}

.newsletter-form {
    display: flex;
    gap: var(--space-2);
}

.newsletter-input {
    flex: 1;
    padding: var(--space-3);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-md);
    font-size: var(--text-sm);
    font-family: inherit;
}

.newsletter-input:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.newsletter-btn {
    padding: var(--space-3) var(--space-4);
    background-color: var(--color-primary);
    color: white;
    border: none;
    border-radius: var(--border-radius-md);
    font-size: var(--text-sm);
    font-weight: 600;
    cursor: pointer;
    transition: background-color var(--transition-fast);
    white-space: nowrap;
}

.newsletter-btn:hover {
    background-color: var(--color-primary-dark);
}

.footer-bottom {
    padding-top: var(--space-8);
    border-top: 1px solid var(--color-border-light);
    text-align: center;
}

.copyright {
    font-size: var(--text-sm);
    color: var(--color-text-tertiary);
}

/* ===========================
   ARTICLE TEMPLATE SPECIFIC STYLES
   =========================== */
.article-layout {
    display: grid;
    grid-template-columns: 1fr 280px;
    gap: var(--space-12);
    margin-top: var(--space-12);
}

.article-main {
    min-width: 0;
}

.article-sidebar {
    position: relative;
}

/* Breadcrumbs */
.breadcrumb {
    display: flex;
    align-items: center;
    gap: var(--space-2);
    flex-wrap: wrap;
    list-style: none;
    margin-bottom: var(--space-6);
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
}

.breadcrumb-item {
    display: flex;
    align-items: center;
}

.breadcrumb-item:not(:last-child)::after {
    content: '›';
    margin-left: var(--space-2);
    color: var(--color-text-tertiary);
}

.breadcrumb-link {
    color: var(--color-text-secondary);
}

.breadcrumb-link:hover {
    color: var(--color-primary);
}

/* Article Header */
.article-header {
    margin-bottom: var(--space-10);
}

.article-meta-top {
    display: flex;
    align-items: center;
    gap: var(--space-4);
    margin-bottom: var(--space-4);
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
}

.article-title-main {
    font-size: var(--text-5xl);
    font-weight: 800;
    line-height: 1.1;
    margin-bottom: var(--space-6);
}

.article-excerpt {
    font-size: var(--text-xl);
    color: var(--color-text-secondary);
    line-height: 1.6;
}

/* Article Content */
.article-body {
    font-size: var(--text-lg);
    line-height: 1.8;
    color: var(--color-text-primary);
}

.article-body h2 {
    margin-top: var(--space-12);
    margin-bottom: var(--space-6);
    scroll-margin-top: 100px;
}

.article-body h3 {
    margin-top: var(--space-10);
    margin-bottom: var(--space-4);
    scroll-margin-top: 100px;
}

.article-body p {
    margin-bottom: var(--space-6);
}

.article-body ul,
.article-body ol {
    margin-bottom: var(--space-6);
    padding-left: var(--space-8);
}

.article-body li {
    margin-bottom: var(--space-3);
}

.article-body a {
    font-weight: 500;
    text-decoration: underline;
    text-decoration-thickness: 1px;
    text-underline-offset: 2px;
}

.article-body strong {
    font-weight: 700;
    color: var(--color-text-primary);
}

.article-body code {
    background-color: var(--color-background-alt);
    padding: var(--space-1) var(--space-2);
    border-radius: var(--border-radius-sm);
    font-family: var(--font-mono);
    font-size: 0.9em;
}

/* Table of Contents */
.toc {
    position: sticky;
    top: 100px;
    background: white;
    border: 1px solid var(--color-border-light);
    border-radius: var(--border-radius-lg);
    padding: var(--space-6);
    max-height: calc(100vh - 120px);
    overflow-y: auto;
}

.toc-title {
    font-size: var(--text-sm);
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-4);
    color: var(--color-text-primary);
}

.toc-list {
    list-style: none;
}

.toc-item {
    margin-bottom: var(--space-3);
}

.toc-link {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    display: block;
    padding: var(--space-2) 0;
    border-left: 2px solid transparent;
    padding-left: var(--space-3);
    transition: all var(--transition-fast);
}

.toc-link:hover,
.toc-link.active {
    color: var(--color-primary);
    border-left-color: var(--color-primary);
}

.toc-link-h3 {
    padding-left: var(--space-6);
    font-size: var(--text-xs);
}

/* Author Bio */
.author-bio {
    display: flex;
    gap: var(--space-4);
    padding: var(--space-6);
    background-color: var(--color-background-alt);
    border-radius: var(--border-radius-lg);
    margin-top: var(--space-12);
}

.author-avatar {
    width: 64px;
    height: 64px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
    flex-shrink: 0;
}

.author-info h3 {
    font-size: var(--text-lg);
    margin-bottom: var(--space-2);
}

.author-info p {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    margin-bottom: 0;
}

/* ===========================
   RESPONSIVE DESIGN (Mobile-First)
   =========================== */
@media (max-width: 1024px) {
    .article-layout {
        grid-template-columns: 1fr;
    }

    .article-sidebar {
        order: -1;
    }

    .toc {
        position: static;
        max-height: 400px;
    }
}

@media (max-width: 768px) {
    :root {
        --text-4xl: 2rem;
        --text-3xl: 1.5rem;
        --text-2xl: 1.25rem;
        --space-16: 3rem;
        --space-20: 4rem;
    }

    .mobile-menu-toggle {
        display: block;
    }

    .nav-menu {
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background-color: white;
        flex-direction: column;
        align-items: stretch;
        padding: var(--space-4);
        box-shadow: var(--shadow-lg);
        display: none;
        gap: 0;
    }

    .nav-menu.active {
        display: flex;
    }

    .nav-link {
        padding: var(--space-3) var(--space-4);
    }

    .nav-link.active::after {
        display: none;
    }

    .hero {
        padding: var(--space-12) 0;
    }

    .hero-title {
        font-size: var(--text-3xl);
    }

    .hero-cta {
        flex-direction: column;
    }

    .btn {
        width: 100%;
    }

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

    .footer-grid {
        grid-template-columns: 1fr;
        gap: var(--space-8);
    }

    .newsletter-form {
        flex-direction: column;
    }

    .article-title-main {
        font-size: var(--text-3xl);
    }

    .latest-section .section-header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--space-4);
    }
}

@media (max-width: 480px) {
    .books-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

/* ===========================
   PERFORMANCE OPTIMIZATIONS
   =========================== */
/* Reduce paint on scroll */
.site-header {
    will-change: transform;
}

/* GPU acceleration for transforms */
.article-card,
.book-card,
.guide-item {
    will-change: transform;
}

/* Image lazy loading placeholder */
img.lazy {
    background-color: var(--color-background-alt);
}

/* Print styles */
@media print {
    .site-header,
    .site-footer,
    .toc,
    .ad-placeholder,
    .hero-cta {
        display: none;
    }

    body {
        font-size: 12pt;
    }
}