/* ============================================
   CodeVault - Clean Modern Design
   ============================================ */

/* CSS Variables */
:root {
    --color-bg: #ffffff;
    --color-surface: #f8fafc;
    --color-card: #ffffff;
    --color-border: #e2e8f0;
    --color-text: #1e293b;
    --color-text-secondary: #64748b;
    --color-primary: #3b82f6;
    --color-primary-hover: #2563eb;
    --color-c: #d97706;
    --color-java: #0891b2;
    --color-go: #059669;
    --color-easy: #22c55e;
    --color-medium: #f59e0b;
    --color-hard: #ef4444;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow: 0 1px 3px 0 rgb(0 0 0 / 0.1), 0 1px 2px -1px rgb(0 0 0 / 0.1);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --radius: 8px;
    --radius-lg: 12px;
    --transition: 150ms ease;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* Container */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* ============================================
   Header & Navigation
   ============================================ */
.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(8px);
    border-bottom: 1px solid var(--color-border);
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
    gap: 2rem;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    color: var(--color-text);
    font-weight: 700;
    font-size: 1.25rem;
}

.logo-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    background: var(--color-primary);
    color: white;
    border-radius: var(--radius);
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.875rem;
    font-weight: 700;
}

.nav-search {
    flex: 1;
    max-width: 400px;
}

.search-input {
    width: 100%;
    padding: 0.625rem 1rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    font-size: 0.875rem;
    background: var(--color-surface);
    color: var(--color-text);
    transition: border-color var(--transition), box-shadow var(--transition);
}

.search-input:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.search-input::placeholder {
    color: var(--color-text-secondary);
}

.nav-links {
    display: flex;
    gap: 1.5rem;
}

.nav-link {
    color: var(--color-text-secondary);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.875rem;
    transition: color var(--transition);
}

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

/* ============================================
   Hero Section
   ============================================ */
.hero {
    padding: 5rem 0 4rem;
    background: linear-gradient(180deg, var(--color-surface) 0%, var(--color-bg) 100%);
}

.hero-content {
    max-width: 700px;
}

.hero-title {
    font-size: 2.75rem;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1.25rem;
    color: var(--color-text);
}

.highlight {
    color: var(--color-c);
}

.highlight.java {
    color: var(--color-java);
}

.highlight.go {
    color: var(--color-go);
}

.hero-subtitle {
    font-size: 1.125rem;
    color: var(--color-text-secondary);
    margin-bottom: 2rem;
    line-height: 1.7;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.75rem 1.5rem;
    font-size: 0.875rem;
    font-weight: 600;
    border-radius: var(--radius);
    border: none;
    cursor: pointer;
    text-decoration: none;
    transition: all var(--transition);
}

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

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

/* ============================================
   Filters
   ============================================ */
.filters {
    padding: 1.5rem 0;
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
    position: sticky;
    top: 64px;
    z-index: 50;
}

.filters-wrapper {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    flex-wrap: wrap;
}

.language-filters {
    display: flex;
    gap: 0.5rem;
}

.filter-btn {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
    font-weight: 500;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-card);
    color: var(--color-text-secondary);
    cursor: pointer;
    transition: all var(--transition);
}

.filter-btn:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

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

.select-input {
    padding: 0.5rem 2rem 0.5rem 1rem;
    font-size: 0.875rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: var(--color-card);
    color: var(--color-text);
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%2364748b' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 0.75rem center;
}

.select-input:focus {
    outline: none;
    border-color: var(--color-primary);
}

/* ============================================
   Problems Grid
   ============================================ */
.problems-section {
    padding: 2rem 0 4rem;
    min-height: 50vh;
}

.problems-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1.5rem;
}

.problem-card {
    background: var(--color-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: 1.5rem;
    transition: all var(--transition);
    cursor: pointer;
}

.problem-card:hover {
    border-color: var(--color-primary);
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
}

.card-header {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    gap: 1rem;
    margin-bottom: 0.75rem;
}

.card-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--color-text);
    line-height: 1.4;
}

.difficulty-badge {
    flex-shrink: 0;
    padding: 0.25rem 0.625rem;
    font-size: 0.75rem;
    font-weight: 600;
    border-radius: 9999px;
    text-transform: capitalize;
}

.difficulty-easy {
    background: rgba(34, 197, 94, 0.1);
    color: var(--color-easy);
}

.difficulty-medium {
    background: rgba(245, 158, 11, 0.1);
    color: var(--color-medium);
}

.difficulty-hard {
    background: rgba(239, 68, 68, 0.1);
    color: var(--color-hard);
}

.card-description {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    margin-bottom: 1rem;
    line-height: 1.5;
}

.language-tags {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1.25rem;
}

.lang-tag {
    padding: 0.25rem 0.5rem;
    font-size: 0.75rem;
    font-weight: 600;
    border-radius: 4px;
    font-family: 'JetBrains Mono', monospace;
}

.lang-tag-c {
    background: rgba(217, 119, 6, 0.1);
    color: var(--color-c);
}

.lang-tag-java {
    background: rgba(8, 145, 178, 0.1);
    color: var(--color-java);
}

.lang-tag-go {
    background: rgba(5, 150, 105, 0.1);
    color: var(--color-go);
}

.view-btn {
    width: 100%;
    padding: 0.625rem;
    font-size: 0.875rem;
    font-weight: 500;
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    background: transparent;
    color: var(--color-primary);
    cursor: pointer;
    transition: all var(--transition);
}

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

.no-results {
    display: none;
    text-align: center;
    padding: 3rem;
    color: var(--color-text-secondary);
}

.no-results.visible {
    display: block;
}

/* ============================================
   About Section
   ============================================ */
.about {
    padding: 4rem 0;
    background: var(--color-surface);
}

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

.section-title {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--color-text);
}

.about-text {
    font-size: 1rem;
    color: var(--color-text-secondary);
    margin-bottom: 3rem;
    line-height: 1.7;
}

.features {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
}

.feature {
    text-align: center;
}

.feature-icon {
    font-size: 2rem;
    margin-bottom: 0.75rem;
}

.feature h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--color-text);
}

.feature p {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

/* ============================================
   Footer
   ============================================ */
.footer {
    padding: 2rem 0;
    border-top: 1px solid var(--color-border);
}

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

.footer-text {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.github-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--color-text-secondary);
    text-decoration: none;
    font-size: 0.875rem;
    font-weight: 500;
    transition: color var(--transition);
}

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

/* ============================================
   Modal
   ============================================ */
.modal-overlay {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 200;
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--transition), visibility var(--transition);
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal {
    position: fixed;
    top: 0;
    right: 0;
    width: 100%;
    max-width: 700px;
    height: 100vh;
    background: var(--color-card);
    z-index: 201;
    transform: translateX(100%);
    transition: transform 300ms ease;
    display: flex;
    flex-direction: column;
    box-shadow: var(--shadow-lg);
}

.modal.active {
    transform: translateX(0);
}

.modal-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1.25rem 1.5rem;
    border-bottom: 1px solid var(--color-border);
    flex-shrink: 0;
}

.modal-title {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--color-text);
}

.modal-close {
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    font-size: 1.5rem;
    cursor: pointer;
    border-radius: var(--radius);
    transition: all var(--transition);
}

.modal-close:hover {
    background: var(--color-surface);
    color: var(--color-text);
}

.modal-body {
    flex: 1;
    overflow-y: auto;
    padding: 1.5rem;
}

/* Problem Statement */
.problem-statement {
    background: var(--color-surface);
    border-radius: var(--radius);
    padding: 1.25rem;
    margin-bottom: 1.5rem;
}

.problem-statement h3 {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--color-text-secondary);
    margin-bottom: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.problem-statement p {
    font-size: 0.9375rem;
    color: var(--color-text);
    line-height: 1.7;
}

.complexity-badges {
    display: flex;
    gap: 0.75rem;
    margin-top: 1rem;
}

.complexity-badge {
    padding: 0.375rem 0.75rem;
    background: var(--color-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    font-size: 0.8125rem;
}

.complexity-badge span {
    color: var(--color-text-secondary);
}

.complexity-badge strong {
    color: var(--color-primary);
    font-family: 'JetBrains Mono', monospace;
}

/* Code Tabs */
.code-tabs {
    display: flex;
    gap: 0.25rem;
    margin-bottom: 0;
    background: var(--color-surface);
    padding: 0.25rem;
    border-radius: var(--radius) var(--radius) 0 0;
}

.code-tab {
    padding: 0.5rem 1rem;
    font-size: 0.8125rem;
    font-weight: 500;
    font-family: 'JetBrains Mono', monospace;
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    cursor: pointer;
    border-radius: var(--radius);
    transition: all var(--transition);
}

.code-tab:hover {
    color: var(--color-text);
}

.code-tab.active {
    background: var(--color-card);
    color: var(--color-text);
    box-shadow: var(--shadow-sm);
}

/* Code Block */
.code-block-wrapper {
    position: relative;
    background: #0d1117;
    border-radius: 0 0 var(--radius) var(--radius);
    overflow: hidden;
}

.code-block {
    padding: 1.25rem;
    overflow-x: auto;
}

.code-block pre {
    margin: 0;
}

.code-block code {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.8125rem;
    line-height: 1.6;
}

.copy-btn {
    position: absolute;
    top: 0.75rem;
    right: 0.75rem;
    padding: 0.375rem 0.75rem;
    font-size: 0.75rem;
    font-weight: 500;
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: var(--radius);
    background: rgba(255, 255, 255, 0.1);
    color: rgba(255, 255, 255, 0.8);
    cursor: pointer;
    transition: all var(--transition);
}

.copy-btn:hover {
    background: rgba(255, 255, 255, 0.2);
}

.copy-btn.copied {
    background: var(--color-easy);
    border-color: var(--color-easy);
    color: white;
}

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 1024px) {
    .problems-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    .nav {
        flex-wrap: wrap;
        height: auto;
        padding: 1rem 0;
        gap: 1rem;
    }

    .nav-search {
        order: 3;
        max-width: 100%;
        width: 100%;
    }

    .hero-title {
        font-size: 2rem;
    }

    .filters-wrapper {
        flex-direction: column;
        align-items: stretch;
    }

    .language-filters {
        justify-content: center;
    }

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

    .features {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }

    .footer-content {
        flex-direction: column;
        gap: 1rem;
        text-align: center;
    }

    .modal {
        max-width: 100%;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 1.75rem;
    }

    .hero-subtitle {
        font-size: 1rem;
    }

    .filter-btn {
        padding: 0.375rem 0.75rem;
        font-size: 0.8125rem;
    }
}