/* CSS Variables */
:root {
    --primary: #6366f1;
    --primary-hover: #4f46e5;
    --primary-light: #e0e7ff;
    --secondary: #64748b;
    --secondary-hover: #475569;
    --success: #10b981;
    --success-hover: #059669;
    --error: #ef4444;
    --error-bg: #fef2f2;
    --text: #1e293b;
    --text-light: #64748b;
    --bg: #f8fafc;
    --card: #ffffff;
    --border: #e2e8f0;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.1);
    --radius: 12px;
    --radius-sm: 8px;
    --transition: all 0.2s ease;
}

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

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Skip Link */
.skip-link {
    position: absolute;
    top: -100%;
    left: 0;
    background: var(--primary);
    color: white;
    padding: 0.75rem 1.5rem;
    z-index: 1000;
    text-decoration: none;
    font-weight: 600;
    border-radius: 0 0 var(--radius-sm) 0;
}

.skip-link:focus {
    top: 0;
}

/* Container */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
}

/* Header */
.header {
    background: var(--card);
    border-bottom: 1px solid var(--border);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow);
}

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

.logo {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text);
    text-decoration: none;
}

.logo-icon {
    font-size: 1.8rem;
}

/* Hamburger */
.hamburger {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
    min-width: 44px;
    min-height: 44px;
    align-items: center;
    justify-content: center;
}

.hamburger-line {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--text);
    border-radius: 2px;
    transition: var(--transition);
}

.hamburger[aria-expanded="true"] .hamburger-line:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}

.hamburger[aria-expanded="true"] .hamburger-line:nth-child(2) {
    opacity: 0;
}

.hamburger[aria-expanded="true"] .hamburger-line:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

.nav {
    display: flex;
    gap: 0.5rem;
    flex-wrap: wrap;
}

.nav-link {
    padding: 0.5rem 1rem;
    color: var(--text-light);
    text-decoration: none;
    border-radius: var(--radius-sm);
    font-weight: 500;
    transition: var(--transition);
}

.nav-link:hover,
.nav-link:focus {
    background: var(--primary-light);
    color: var(--primary);
    outline: none;
}

.nav-link.active {
    background: var(--primary);
    color: white;
}

/* Main */
.main {
    flex: 1;
    padding: 2rem 0;
}

/* Hero */
.hero {
    text-align: center;
    margin-bottom: 2rem;
}

.hero-title {
    font-size: clamp(1.8rem, 5vw, 2.5rem);
    font-weight: 800;
    margin-bottom: 0.5rem;
    background: linear-gradient(135deg, var(--primary) 0%, #8b5cf6 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.1rem;
    color: var(--text-light);
}

/* Converter */
.converter {
    background: var(--card);
    border-radius: var(--radius);
    box-shadow: var(--shadow-lg);
    padding: 2rem;
    margin-bottom: 3rem;
}

/* Upload Zone */
.upload-zone {
    border: 2px dashed var(--border);
    border-radius: var(--radius);
    padding: 3rem 2rem;
    text-align: center;
    cursor: pointer;
    transition: var(--transition);
    background: var(--bg);
    position: relative;
}

.upload-zone:hover,
.upload-zone:focus {
    border-color: var(--primary);
    background: var(--primary-light);
    outline: none;
}

.upload-zone.dragover {
    border-color: var(--primary);
    background: var(--primary-light);
    transform: scale(1.02);
}

.upload-zone:focus-visible {
    outline: 3px solid var(--primary);
    outline-offset: 2px;
}

.upload-content {
    pointer-events: none;
}

.upload-icon {
    font-size: 4rem;
    margin-bottom: 1rem;
}

.upload-text {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.upload-subtext {
    color: var(--text-light);
    margin-bottom: 1rem;
}

.upload-limit {
    font-size: 0.875rem;
    color: var(--text-light);
    background: var(--border);
    display: inline-block;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
}

.file-input {
    position: absolute;
    inset: 0;
    opacity: 0;
    cursor: pointer;
}

/* File List */
.file-list {
    margin-top: 1.5rem;
}

.file-item {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 1rem;
    background: var(--bg);
    border-radius: var(--radius-sm);
    margin-bottom: 0.75rem;
    border: 1px solid var(--border);
    animation: slideIn 0.3s ease;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.file-icon {
    width: 60px;
    height: 60px;
    border-radius: var(--radius-sm);
    background: var(--primary-light);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    flex-shrink: 0;
}

.file-info {
    flex: 1;
    min-width: 0;
}

.file-name {
    font-weight: 600;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.file-size {
    font-size: 0.875rem;
    color: var(--text-light);
}

.file-page-count {
    font-size: 0.8rem;
    color: var(--primary);
    font-weight: 500;
}

.file-remove {
    background: none;
    border: none;
    padding: 0.5rem;
    cursor: pointer;
    color: var(--text-light);
    font-size: 1.25rem;
    border-radius: var(--radius-sm);
    transition: var(--transition);
    min-width: 44px;
    min-height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.file-remove:hover,
.file-remove:focus {
    background: var(--error-bg);
    color: var(--error);
    outline: none;
}

/* Error Message */
.error-message {
    display: none;
    padding: 1rem;
    background: var(--error-bg);
    color: var(--error);
    border-radius: var(--radius-sm);
    margin-top: 1rem;
    border: 1px solid var(--error);
}

.error-message.show {
    display: block;
    animation: shake 0.5s ease;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

/* Actions */
.actions {
    display: flex;
    gap: 1rem;
    margin-top: 1.5rem;
    flex-wrap: wrap;
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0.875rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
    text-decoration: none;
    min-height: 44px;
}

.btn:focus-visible {
    outline: 3px solid var(--primary);
    outline-offset: 2px;
}

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

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

.btn-primary:disabled {
    background: var(--secondary);
    cursor: not-allowed;
    transform: none;
}

.btn-secondary {
    background: var(--bg);
    color: var(--text);
    border: 1px solid var(--border);
}

.btn-secondary:hover,
.btn-secondary:focus {
    background: var(--border);
}

.btn-download {
    background: var(--success);
    color: white;
    margin-top: 1.5rem;
}

.btn-download:hover,
.btn-download:focus {
    background: var(--success-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-icon {
    font-size: 1.1rem;
}

/* Progress */
.progress {
    margin-top: 1.5rem;
}

.progress-bar {
    height: 8px;
    background: var(--border);
    border-radius: 4px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), #8b5cf6);
    width: 0%;
    transition: width 0.3s ease;
}

.progress-text {
    text-align: center;
    margin-top: 0.75rem;
    color: var(--text-light);
    font-size: 0.9rem;
}

/* Results */
.results {
    margin-top: 2rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border);
}

.results-title {
    font-size: 1.25rem;
    margin-bottom: 1rem;
}

.results-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    gap: 1rem;
}

.result-item {
    background: var(--bg);
    border-radius: var(--radius-sm);
    padding: 1rem;
    text-align: center;
    border: 1px solid var(--border);
    transition: var(--transition);
}

.result-item:hover {
    border-color: var(--primary);
}

.result-preview {
    width: 100%;
    height: 180px;
    object-fit: contain;
    margin-bottom: 0.75rem;
    border-radius: var(--radius-sm);
    /* Checkerboard pattern for transparency */
    background-image:
        linear-gradient(45deg, #e2e8f0 25%, transparent 25%),
        linear-gradient(-45deg, #e2e8f0 25%, transparent 25%),
        linear-gradient(45deg, transparent 75%, #e2e8f0 75%),
        linear-gradient(-45deg, transparent 75%, #e2e8f0 75%);
    background-size: 20px 20px;
    background-position: 0 0, 0 10px, 10px -10px, -10px 0px;
}

.result-name {
    font-weight: 600;
    font-size: 0.9rem;
    margin-bottom: 0.25rem;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.result-page {
    font-size: 0.8rem;
    color: var(--primary);
    margin-bottom: 0.25rem;
}

.result-size {
    font-size: 0.8rem;
    color: var(--text-light);
    margin-bottom: 0.75rem;
}

.result-download {
    display: inline-flex;
    align-items: center;
    gap: 0.25rem;
    padding: 0.5rem 1rem;
    background: var(--primary);
    color: white;
    text-decoration: none;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 500;
    transition: var(--transition);
    min-height: 44px;
}

.result-download:hover,
.result-download:focus {
    background: var(--primary-hover);
}

/* Features */
.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 1.5rem;
    margin-bottom: 3rem;
}

.feature {
    background: var(--card);
    padding: 1.5rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    text-align: center;
}

.feature-icon {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.feature-title {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.feature-desc {
    font-size: 0.9rem;
    color: var(--text-light);
}

/* FAQ */
.faq {
    margin-bottom: 3rem;
}

.faq-title {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    text-align: center;
}

.faq-item {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    margin-bottom: 0.75rem;
    overflow: hidden;
}

.faq-question {
    padding: 1rem 1.25rem;
    font-weight: 600;
    cursor: pointer;
    list-style: none;
    display: flex;
    justify-content: space-between;
    align-items: center;
    min-height: 44px;
    transition: var(--transition);
}

.faq-question::-webkit-details-marker {
    display: none;
}

.faq-question::after {
    content: '+';
    font-size: 1.5rem;
    color: var(--primary);
    transition: transform 0.2s;
}

.faq-item[open] .faq-question::after {
    content: '−';
}

.faq-question:hover {
    background: var(--bg);
}

.faq-answer {
    padding: 0 1.25rem 1rem;
    color: var(--text-light);
    line-height: 1.7;
}

/* Footer */
.footer {
    background: var(--card);
    border-top: 1px solid var(--border);
    padding: 1.5rem 0;
    margin-top: auto;
}

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

.footer-text {
    font-size: 0.9rem;
    color: var(--text-light);
}

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

.footer-links a {
    color: var(--text-light);
    text-decoration: none;
    font-size: 0.9rem;
    transition: var(--transition);
}

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

/* Focus Visible */
:focus-visible {
    outline: 3px solid var(--primary);
    outline-offset: 2px;
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* Responsive: Tablet */
@media (max-width: 768px) {
    .hamburger {
        display: flex;
    }

    .nav {
        display: none;
        width: 100%;
        flex-direction: column;
        gap: 0.25rem;
    }

    .nav.open {
        display: flex;
    }

    .nav-link {
        width: 100%;
        padding: 0.75rem 1rem;
    }

    .header .container {
        flex-wrap: wrap;
    }

    .converter {
        padding: 1.5rem;
    }

    .upload-zone {
        padding: 2rem 1rem;
    }

    .results-grid {
        grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
    }

    .footer .container {
        flex-direction: column;
        text-align: center;
    }
}

/* Responsive: Small phones */
@media (max-width: 480px) {
    .hero-title {
        font-size: 1.5rem;
    }

    .converter {
        padding: 1rem;
    }

    .upload-zone {
        padding: 1.5rem 1rem;
    }

    .upload-icon {
        font-size: 3rem;
    }

    .upload-text {
        font-size: 1.1rem;
    }

    .actions {
        flex-direction: column;
    }

    .btn {
        width: 100%;
    }

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

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

    .file-item {
        flex-wrap: wrap;
    }

    .file-icon {
        width: 50px;
        height: 50px;
        font-size: 1.5rem;
    }
}