/* OpenAI-inspired Design System */

/* CSS Variables - OpenAI Style */
:root {
    /* Colors - Dark Theme */
    --color-bg: #0d0d0d;
    --color-bg-secondary: #111111;
    --color-bg-tertiary: #1a1a1a;
    --color-surface: #202123;
    --color-surface-hover: #2d2d2d;
    
    /* Text Colors */
    --color-text-primary: #ffffff;
    --color-text-secondary: #8e8e8e;
    --color-text-tertiary: #5a5a5a;
    
    /* Accent - OpenAI Green */
    --color-accent: #10a37f;
    --color-accent-hover: #0d8c6d;
    --color-accent-light: #19c59f;
    
    /* Borders */
    --color-border: #2d2d2d;
    --color-border-hover: #404040;
    
    /* Gradients */
    --gradient-hero: linear-gradient(180deg, #0d0d0d 0%, #111111 100%);
    --gradient-accent: linear-gradient(90deg, #10a37f 0%, #19c59f 100%);
    
    /* Typography */
    --font-primary: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --font-mono: "SF Mono", "Monaco", "Inconsolata", "Fira Code", monospace;
    
    /* Font Sizes - Large Scale */
    --text-xs: 0.75rem;
    --text-sm: 0.875rem;
    --text-base: 1rem;
    --text-lg: 1.125rem;
    --text-xl: 1.5rem;
    --text-2xl: 2rem;
    --text-3xl: 2.5rem;
    --text-4xl: 3.5rem;
    --text-5xl: 4.5rem;
    
    /* Spacing */
    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-5: 1.25rem;
    --space-6: 1.5rem;
    --space-8: 2rem;
    --space-10: 2.5rem;
    --space-12: 3rem;
    --space-16: 4rem;
    --space-20: 5rem;
    --space-24: 6rem;
    --space-32: 8rem;
    
    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 200ms ease;
    --transition-slow: 300ms ease;
}

/* Reset */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-primary);
    font-size: var(--text-base);
    line-height: 1.5;
    color: var(--color-text-primary);
    background-color: var(--color-bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Container */
.container {
    width: 100%;
    max-width: 75rem;
    margin: 0 auto;
    padding: 0 var(--space-6);
}

/* Navigation - OpenAI Style */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    background: rgba(13, 13, 13, 0.8);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--color-border);
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 4rem;
}

.nav-logo {
    font-size: var(--text-xl);
    font-weight: 600;
    color: var(--color-text-primary);
    text-decoration: none;
    letter-spacing: -0.02em;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--space-8);
}

.nav-link {
    font-size: var(--text-sm);
    font-weight: 400;
    color: var(--color-text-secondary);
    text-decoration: none;
    transition: color var(--transition-fast);
}

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

/* Hero Section - Large Typography */
.hero {
    min-height: 80vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    padding: var(--space-32) var(--space-6);
    background: var(--gradient-hero);
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: radial-gradient(ellipse at center, rgba(16, 163, 127, 0.1) 0%, transparent 70%);
    pointer-events: none;
}

.hero-content {
    position: relative;
    z-index: 1;
    max-width: 48rem;
}

.hero-title {
    font-size: var(--text-5xl);
    font-weight: 600;
    line-height: 1.1;
    letter-spacing: -0.03em;
    margin-bottom: var(--space-6);
    background: linear-gradient(180deg, #ffffff 0%, #8e8e8e 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: var(--text-xl);
    color: var(--color-text-secondary);
    margin-bottom: var(--space-8);
    font-weight: 400;
}

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

/* Buttons - OpenAI Style */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--space-3) var(--space-6);
    font-family: var(--font-primary);
    font-size: var(--text-sm);
    font-weight: 500;
    text-decoration: none;
    border-radius: 0.375rem;
    cursor: pointer;
    transition: all var(--transition-fast);
    border: 1px solid transparent;
}

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

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

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

.btn-secondary:hover {
    background: var(--color-surface-hover);
    border-color: var(--color-border-hover);
}

/* Page Header */
.page-header {
    padding: var(--space-32) var(--space-6) var(--space-16);
    text-align: center;
    background: var(--color-bg);
}

.page-header h1 {
    font-size: var(--text-4xl);
    font-weight: 600;
    line-height: 1.1;
    letter-spacing: -0.02em;
    margin-bottom: var(--space-4);
}

.page-header p {
    font-size: var(--text-lg);
    color: var(--color-text-secondary);
}

/* Diary List - Cards */
.diary-content {
    padding: var(--space-16) var(--space-6);
    background: var(--color-bg);
}

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

.diary-header h2 {
    font-size: var(--text-3xl);
    font-weight: 600;
    color: var(--color-text-primary);
}

.diary-list {
    display: flex;
    flex-direction: column;
    gap: var(--space-4);
    max-width: 48rem;
    margin: 0 auto;
}

.diary-card-link {
    display: block;
    text-decoration: none;
    color: inherit;
}

.diary-card {
    display: flex;
    gap: var(--space-6);
    padding: var(--space-6);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 0.75rem;
    transition: all var(--transition-base);
}

.diary-card:hover {
    background: var(--color-surface-hover);
    border-color: var(--color-border-hover);
    transform: translateY(-2px);
}

/* Date Badge - Clean Design */
.diary-date {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-width: 4rem;
    padding: var(--space-3) var(--space-2);
    background: var(--color-bg-tertiary);
    border-radius: 0.5rem;
}

.date-day {
    font-size: var(--text-2xl);
    font-weight: 700;
    line-height: 1;
    color: var(--color-text-primary);
}

.date-month {
    font-size: var(--text-xs);
    font-weight: 500;
    color: var(--color-text-secondary);
    margin-top: var(--space-1);
}

.date-time {
    font-size: var(--text-xs);
    font-weight: 500;
    color: var(--color-accent);
    margin-top: var(--space-2);
}

/* Diary Body */
.diary-body {
    flex: 1;
}

.diary-title {
    font-size: var(--text-xl);
    font-weight: 600;
    line-height: 1.3;
    color: var(--color-text-primary);
    margin-bottom: var(--space-2);
}

.diary-excerpt {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin-bottom: var(--space-2);
}

.diary-thoughts-preview {
    font-size: var(--text-xs);
    color: var(--color-accent);
    padding: var(--space-2) var(--space-3);
    background: rgba(16, 163, 127, 0.1);
    border-radius: 0.375rem;
    border-left: 3px solid var(--color-accent);
}

.thoughts-label {
    font-weight: 600;
}

/* Diary Detail */
.diary-detail-header {
    padding: var(--space-32) var(--space-6) var(--space-12);
    text-align: center;
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
}

.back-link {
    display: inline-block;
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    text-decoration: none;
    margin-bottom: var(--space-8);
    transition: color var(--transition-fast);
}

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

.diary-meta {
    max-width: 48rem;
    margin: 0 auto;
}

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

.diary-detail-title {
    font-size: var(--text-4xl);
    font-weight: 600;
    line-height: 1.1;
    letter-spacing: -0.02em;
}

.diary-detail-content {
    padding: var(--space-16) var(--space-6);
    background: var(--color-bg);
}

.diary-article {
    max-width: 48rem;
    margin: 0 auto;
}

.diary-section {
    margin-bottom: var(--space-12);
}

.diary-section h2 {
    font-size: var(--text-2xl);
    font-weight: 600;
    margin-bottom: var(--space-4);
    color: var(--color-text-primary);
}

.diary-text {
    font-size: var(--text-base);
    line-height: 1.8;
    color: var(--color-text-secondary);
}

.diary-text h3 {
    font-size: var(--text-xl);
    font-weight: 600;
    margin-top: var(--space-8);
    margin-bottom: var(--space-3);
    color: var(--color-accent);
}

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

.diary-text ul,
.diary-text ol {
    margin-left: var(--space-6);
    margin-bottom: var(--space-4);
}

.diary-text li {
    margin-bottom: var(--space-2);
}

/* Thoughts Section */
.thoughts-section {
    background: var(--color-surface);
    padding: var(--space-8);
    border-radius: 0.75rem;
    border: 1px solid var(--color-border);
    margin-top: var(--space-12);
}

.thoughts-section h2 {
    color: var(--color-accent);
}

.thoughts-content {
    color: var(--color-text-secondary);
}

/* Nav Cards Section */
.nav-cards {
    padding: var(--space-24) var(--space-6);
    background: var(--color-bg);
}

.nav-cards .section-title {
    font-size: var(--text-3xl);
    font-weight: 600;
    text-align: center;
    margin-bottom: var(--space-12);
    color: var(--color-text-primary);
}

.nav-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(18rem, 1fr));
    gap: var(--space-6);
    max-width: 64rem;
    margin: 0 auto;
}

.nav-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: var(--space-8);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 1rem;
    text-decoration: none;
    text-align: center;
    transition: all var(--transition-base);
}

.nav-card:hover {
    background: var(--color-surface-hover);
    border-color: var(--color-accent);
    transform: translateY(-4px);
    box-shadow: 0 20px 40px rgba(16, 163, 127, 0.1);
}

.nav-card .nav-icon {
    font-size: 3rem;
    margin-bottom: var(--space-4);
}

.nav-card h3 {
    font-size: var(--text-xl);
    font-weight: 600;
    color: var(--color-text-primary);
    margin-bottom: var(--space-2);
}

.nav-card p {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
}

/* Features Section */
.features {
    padding: var(--space-24) var(--space-6);
    background: var(--color-bg-secondary);
}

.section-title {
    font-size: var(--text-3xl);
    font-weight: 600;
    text-align: center;
    margin-bottom: var(--space-12);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(16rem, 1fr));
    gap: var(--space-6);
}

.feature-card {
    padding: var(--space-6);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 0.75rem;
    text-align: center;
    transition: all var(--transition-base);
}

.feature-card:hover {
    background: var(--color-surface-hover);
    transform: translateY(-4px);
}

.feature-icon {
    font-size: 2.5rem;
    margin-bottom: var(--space-4);
}

.feature-card h3 {
    font-size: var(--text-lg);
    font-weight: 600;
    margin-bottom: var(--space-2);
}

.feature-card p {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
}

/* API Demo Section */
.api-demo {
    padding: var(--space-24) var(--space-6);
    background: var(--color-bg);
    text-align: center;
}

.section-subtitle {
    font-size: var(--text-lg);
    color: var(--color-text-secondary);
    margin-bottom: var(--space-6);
}

.api-response {
    margin-top: var(--space-6);
    padding: var(--space-6);
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 0.75rem;
    text-align: left;
    max-width: 48rem;
    margin-left: auto;
    margin-right: auto;
    font-family: var(--font-mono);
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
    min-height: 100px;
}

/* Footer */
.footer {
    padding: var(--space-12) var(--space-6);
    text-align: center;
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-border);
}

.footer p {
    font-size: var(--text-sm);
    color: var(--color-text-secondary);
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: var(--space-16) var(--space-6);
    background: var(--color-surface);
    border: 1px dashed var(--color-border);
    border-radius: 0.75rem;
}

.empty-icon {
    font-size: 3rem;
    margin-bottom: var(--space-4);
    opacity: 0.5;
}

.empty-state h3 {
    font-size: var(--text-xl);
    font-weight: 600;
    margin-bottom: var(--space-2);
}

.empty-state p {
    color: var(--color-text-secondary);
}

/* Responsive */
@media (max-width: 768px) {
    .hero {
        padding: var(--space-24) var(--space-4);
    }
    
    .hero-title {
        font-size: var(--text-3xl);
    }
    
    .hero-subtitle {
        font-size: var(--text-lg);
    }
    
    .page-header {
        padding: var(--space-24) var(--space-4) var(--space-12);
    }
    
    .page-header h1 {
        font-size: var(--text-2xl);
    }
    
    .diary-card {
        flex-direction: column;
        gap: var(--space-4);
        padding: var(--space-4);
    }
    
    .diary-date {
        flex-direction: row;
        align-items: center;
        justify-content: flex-start;
        gap: var(--space-1);
        min-width: auto;
        padding: var(--space-2) var(--space-3);
        background: transparent;
        border: none;
    }
    
    .date-day {
        font-size: var(--text-base);
        font-weight: 600;
    }
    
    .date-month {
        font-size: var(--text-xs);
        margin-top: 0;
        color: var(--color-text-tertiary);
    }
    
    .date-time {
        margin: 0 0 0 var(--space-2);
        padding: var(--space-1) var(--space-2);
        background: var(--color-bg-tertiary);
        border-radius: 0.25rem;
        font-size: var(--text-xs);
        font-weight: 500;
    }
    
    .diary-title {
        font-size: var(--text-lg);
    }
    
    .container {
        padding: 0 var(--space-4);
    }
    
    .nav-menu {
        display: none;
    }
}

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

.diary-card {
    animation: fadeIn 0.5s ease-out;
}

/* Selection */
::selection {
    background: rgba(16, 163, 127, 0.3);
    color: var(--color-text-primary);
}

/* Scrollbar - Dark Theme */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--color-bg-secondary);
}

::-webkit-scrollbar-thumb {
    background: var(--color-border);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--color-border-hover);
}