:root {
    --primary: #1d4ed8;
    --primary-dark: #1e3a8a;
    --primary-light: #60a5fa;
    --secondary: #0891b2;
    --success: #16a34a;
    --error: #dc2626;
    --warning: #d97706;
    --bg-primary: #ffffff;
    --bg-secondary: #f7fafc;
    --bg-tertiary: #eaf1fb;
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-light: #94a3b8;
    --border: #dbe7f5;
    --shadow-sm: 0 10px 30px rgba(15, 23, 42, 0.06);
    --shadow-md: 0 18px 42px rgba(15, 23, 42, 0.1);
    --shadow-lg: 0 28px 70px rgba(15, 23, 42, 0.16);
    --radius-sm: 10px;
    --radius-md: 16px;
    --radius-lg: 24px;
    --radius-xl: 32px;
    --transition: all 0.25s ease;
}

html {
    box-sizing: border-box;
    scroll-behavior: smooth;
    scroll-padding-top: 88px;
}

*, *::before, *::after {
    box-sizing: inherit;
}

body {
    margin: 0;
    font-family: "Segoe UI", "Helvetica Neue", Arial, sans-serif;
    color: var(--text-primary);
    background:
        radial-gradient(circle at top, rgba(96, 165, 250, 0.12), transparent 28rem),
        linear-gradient(180deg, #f8fbff 0%, #eef5fb 100%);
    line-height: 1.6;
}

.site-shell {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.skip-link {
    position: fixed;
    top: 16px;
    left: 16px;
    padding: 10px 16px;
    background: var(--text-primary);
    color: #ffffff;
    border-radius: 999px;
    text-decoration: none;
    transform: translateY(-140%);
    transition: transform 0.2s ease;
    z-index: 2000;
}

.skip-link:focus {
    transform: translateY(0);
}

.container {
    width: min(1120px, calc(100% - 40px));
    margin: 0 auto;
}

.site-header {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.88);
    backdrop-filter: blur(18px);
    border-bottom: 1px solid rgba(219, 231, 245, 0.9);
}

.navbar {
    width: min(1120px, calc(100% - 40px));
    margin: 0 auto;
}

.nav-container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    min-height: 72px;
}

.nav-brand {
    display: flex;
    align-items: center;
    gap: 10px;
    color: var(--text-primary);
    text-decoration: none;
    font-weight: 700;
    font-size: 1.125rem;
}

.brand-icon {
    font-size: 1.4rem;
}

.nav-menu {
    display: flex;
    align-items: center;
    gap: 8px;
    list-style: none;
    margin: 0;
    padding: 0;
}

.nav-link {
    display: inline-flex;
    align-items: center;
    padding: 10px 14px;
    border-radius: 999px;
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 600;
    transition: var(--transition);
}

.nav-link:hover,
.nav-link:focus-visible {
    color: var(--primary);
    background: rgba(96, 165, 250, 0.12);
}

.nav-toggle {
    display: none;
    border: none;
    background: transparent;
    padding: 8px;
    cursor: pointer;
}

.hamburger {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    position: relative;
    transition: var(--transition);
}

.hamburger::before,
.hamburger::after {
    content: "";
    position: absolute;
    left: 0;
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    transition: var(--transition);
}

.hamburger::before {
    top: -8px;
}

.hamburger::after {
    bottom: -8px;
}

.nav-toggle.active .hamburger {
    background: transparent;
}

.nav-toggle.active .hamburger::before {
    top: 0;
    transform: rotate(45deg);
}

.nav-toggle.active .hamburger::after {
    bottom: 0;
    transform: rotate(-45deg);
}

.main-content {
    flex: 1;
}

.hero-section {
    padding: clamp(56px, 7vw, 96px) 0;
    color: #ffffff;
    background:
        radial-gradient(circle at top left, rgba(103, 232, 249, 0.22), transparent 24rem),
        linear-gradient(135deg, #0f172a 0%, #1d4ed8 58%, #0891b2 100%);
}

.hero-grid {
    display: grid;
    grid-template-columns: minmax(0, 1.15fr) minmax(320px, 460px);
    gap: 40px;
    align-items: center;
}

.hero-copy {
    text-align: left;
}

.hero-kicker {
    margin: 0 0 18px;
    font-size: 0.82rem;
    font-weight: 700;
    letter-spacing: 0.14em;
    text-transform: uppercase;
    color: rgba(255, 255, 255, 0.78);
}

.hero-section h1 {
    margin: 0 0 18px;
    font-size: clamp(2.4rem, 5vw, 4rem);
    line-height: 1.08;
    letter-spacing: -0.03em;
}

.hero-subtitle {
    max-width: 640px;
    margin: 0 0 28px;
    font-size: 1.1rem;
    color: rgba(255, 255, 255, 0.84);
}

.hero-highlights {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    list-style: none;
    margin: 0;
    padding: 0;
}

.hero-highlights li {
    padding: 10px 14px;
    border: 1px solid rgba(255, 255, 255, 0.18);
    border-radius: 999px;
    background: rgba(255, 255, 255, 0.12);
    font-size: 0.95rem;
}

.converter-panel {
    padding: 24px;
    border: 1px solid rgba(255, 255, 255, 0.18);
    border-radius: var(--radius-xl);
    background: rgba(7, 16, 33, 0.2);
    box-shadow: var(--shadow-lg);
}

.converter-panel h2 {
    margin: 0 0 8px;
    font-size: 1.35rem;
}

.converter-panel-intro {
    margin: 0 0 20px;
    color: rgba(255, 255, 255, 0.8);
    font-size: 0.95rem;
}

.upload-area {
    margin: 0 0 20px;
    padding: 42px 24px;
    border: 2px dashed rgba(255, 255, 255, 0.36);
    border-radius: var(--radius-lg);
    background: rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(10px);
    cursor: pointer;
    text-align: center;
    transition: var(--transition);
}

.upload-area:hover,
.upload-area.dragover {
    background: rgba(255, 255, 255, 0.16);
    border-color: rgba(255, 255, 255, 0.64);
}

.upload-icon {
    margin-bottom: 16px;
    opacity: 0.92;
}

.upload-icon svg {
    stroke: #ffffff;
}

.upload-text {
    margin: 0 0 8px;
    font-size: 1.1rem;
    font-weight: 600;
}

.upload-subtext {
    margin: 0 0 16px;
    color: rgba(255, 255, 255, 0.72);
}

.upload-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 12px 24px;
    border-radius: 999px;
    background: #ffffff;
    color: var(--primary-dark);
    font-weight: 700;
    cursor: pointer;
    transition: var(--transition);
    text-decoration: none;
}

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

.file-info {
    margin: 16px 0 0;
    color: rgba(255, 255, 255, 0.7);
    font-size: 0.875rem;
}

.file-preview {
    margin: 0 0 20px;
}

.file-info-box {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 16px 18px;
    border-radius: var(--radius-md);
    background: rgba(255, 255, 255, 0.95);
    box-shadow: var(--shadow-sm);
}

.file-icon {
    font-size: 1.9rem;
}

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

.file-name {
    margin: 0;
    font-weight: 700;
    overflow-wrap: anywhere;
}

.file-size {
    margin: 4px 0 0;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.remove-file-btn {
    border: none;
    background: transparent;
    color: var(--text-light);
    font-size: 1.5rem;
    cursor: pointer;
    transition: var(--transition);
}

.remove-file-btn:hover {
    color: var(--error);
}

.progress-container {
    margin: 0 0 20px;
}

.progress-bar {
    height: 8px;
    overflow: hidden;
    border-radius: 999px;
    background: rgba(255, 255, 255, 0.16);
}

.progress-fill {
    width: 0;
    height: 100%;
    border-radius: 999px;
    background: linear-gradient(90deg, #93c5fd 0%, #67e8f9 100%);
    transition: width 0.25s ease;
}

.progress-text {
    margin: 12px 0 0;
    font-size: 0.9rem;
    color: rgba(255, 255, 255, 0.82);
}

.error-message {
    margin: 0 0 20px;
    padding: 14px 16px;
    border-radius: var(--radius-md);
    background: rgba(248, 113, 113, 0.18);
    border: 1px solid rgba(248, 113, 113, 0.36);
    color: #fee2e2;
}

.convert-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 100%;
    padding: 16px 24px;
    border: none;
    border-radius: 999px;
    background: #ffffff;
    color: var(--primary-dark);
    font-size: 1.05rem;
    font-weight: 700;
    cursor: pointer;
    transition: var(--transition);
    box-shadow: var(--shadow-md);
}

.convert-btn:hover:not(:disabled) {
    transform: translateY(-1px);
    box-shadow: var(--shadow-lg);
}

.convert-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.btn-loading {
    display: flex;
    align-items: center;
    gap: 8px;
}

.spinner {
    width: 18px;
    height: 18px;
    border: 2px solid rgba(29, 78, 216, 0.22);
    border-top-color: var(--primary);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to {
        transform: rotate(360deg);
    }
}

.success-message {
    margin: 20px 0 0;
    padding: 24px;
    border-radius: var(--radius-lg);
    background: rgba(255, 255, 255, 0.95);
    text-align: center;
    box-shadow: var(--shadow-md);
}

.success-icon {
    margin: 0 0 8px;
    color: var(--success);
    font-size: 2.5rem;
}

.success-message p {
    margin: 0 0 18px;
    color: var(--text-primary);
    font-weight: 600;
}

.download-btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 14px 24px;
    border-radius: 999px;
    background: var(--success);
    color: #ffffff;
    text-decoration: none;
    font-weight: 700;
    transition: var(--transition);
}

.download-btn:hover {
    background: #15803d;
    transform: translateY(-1px);
}

.noscript-note {
    margin: 16px 0 0;
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.76);
}

.content-section,
.features-section,
.how-to-section,
.faq-section {
    padding: 80px 0;
}

.content-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 24px;
}

.content-card {
    padding: 30px;
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    background: rgba(255, 255, 255, 0.9);
    box-shadow: var(--shadow-sm);
}

.content-card h2 {
    margin: 0 0 14px;
    font-size: 1.5rem;
    line-height: 1.2;
}

.content-card p {
    margin: 0 0 14px;
    color: var(--text-secondary);
}

.content-card p:last-child {
    margin-bottom: 0;
}

.content-list {
    margin: 0;
    padding-left: 20px;
    color: var(--text-secondary);
}

.content-list li + li {
    margin-top: 10px;
}

.features-section,
.faq-section,
.privacy-section,
.error-section {
    background: rgba(255, 255, 255, 0.82);
}

.how-to-section {
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.5) 0%, rgba(234, 241, 251, 0.9) 100%);
}

.section-heading {
    max-width: 720px;
    margin: 0 auto 48px;
    text-align: center;
}

.section-heading h2 {
    margin: 0 0 12px;
    font-size: 2rem;
    line-height: 1.15;
}

.section-heading p {
    margin: 0;
    color: var(--text-secondary);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 24px;
}

.feature-card {
    padding: 28px 24px;
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    background: var(--bg-secondary);
    box-shadow: var(--shadow-sm);
    transition: var(--transition);
}

.feature-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
    border-color: rgba(96, 165, 250, 0.6);
}

.feature-icon {
    margin-bottom: 16px;
    font-size: 2.2rem;
}

.feature-card h3 {
    margin: 0 0 10px;
    font-size: 1.15rem;
}

.feature-card p {
    margin: 0;
    color: var(--text-secondary);
}

.steps-container {
    max-width: 860px;
    margin: 0 auto;
    display: grid;
    gap: 20px;
}

.step {
    display: grid;
    grid-template-columns: 52px 1fr;
    gap: 24px;
    align-items: flex-start;
    padding: 24px;
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    background: rgba(255, 255, 255, 0.84);
    box-shadow: var(--shadow-sm);
}

.step-number {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 52px;
    height: 52px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: #ffffff;
    font-size: 1.15rem;
    font-weight: 700;
}

.step-content h3 {
    margin: 0 0 8px;
    font-size: 1.2rem;
}

.step-content p {
    margin: 0;
    color: var(--text-secondary);
}

.faq-list {
    max-width: 860px;
    margin: 0 auto;
    border-top: 1px solid var(--border);
}

.faq-item {
    border-bottom: 1px solid var(--border);
}

.faq-question {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    padding: 22px 0;
    border: none;
    background: transparent;
    color: var(--text-primary);
    font-size: 1.05rem;
    font-weight: 700;
    text-align: left;
    cursor: pointer;
}

.faq-question:hover,
.faq-question:focus-visible {
    color: var(--primary);
}

.faq-toggle {
    color: var(--text-secondary);
    font-size: 0.9rem;
    transition: transform 0.25s ease;
}

.faq-question[aria-expanded="true"] .faq-toggle {
    transform: rotate(180deg);
}

.faq-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.25s ease;
}

.faq-answer p {
    margin: 0;
    padding: 0 0 22px;
    color: var(--text-secondary);
}

.faq-item.active .faq-answer {
    max-height: 220px;
}

.site-footer {
    padding: 56px 0 20px;
    background: #0f172a;
    color: #ffffff;
}

.footer-container {
    width: min(1120px, calc(100% - 40px));
    margin: 0 auto 36px;
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: 32px;
}

.footer-section h3 {
    margin: 0 0 14px;
    font-size: 1.1rem;
}

.footer-section p {
    margin: 0;
    color: rgba(255, 255, 255, 0.72);
}

.footer-section ul {
    list-style: none;
    margin: 0;
    padding: 0;
}

.footer-section li + li {
    margin-top: 8px;
}

.footer-section a {
    color: rgba(255, 255, 255, 0.76);
    text-decoration: none;
}

.footer-section a:hover,
.footer-section a:focus-visible {
    color: #ffffff;
}

.footer-bottom {
    width: min(1120px, calc(100% - 40px));
    margin: 0 auto;
    padding-top: 20px;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    text-align: center;
}

.footer-bottom p {
    margin: 0;
    color: rgba(255, 255, 255, 0.54);
    font-size: 0.88rem;
}

.privacy-section,
.error-section {
    padding: 64px 0;
    flex: 1;
}

.privacy-section h1,
.error-section h1 {
    margin: 0 0 8px;
    font-size: 2rem;
}

.last-updated {
    margin: 0 0 32px;
    color: var(--text-secondary);
}

.privacy-content h2 {
    margin: 30px 0 12px;
    font-size: 1.35rem;
}

.privacy-content p {
    margin: 0 0 16px;
    color: var(--text-secondary);
}

.privacy-content a,
.error-section .back-link {
    color: var(--primary);
    text-decoration: none;
}

.privacy-content a:hover,
.error-section .back-link:hover {
    text-decoration: underline;
}

.error-section p {
    margin: 0;
    color: var(--text-secondary);
}

.error-section .back-link {
    display: inline-block;
    margin-top: 20px;
    font-weight: 600;
}

@media (max-width: 992px) {
    .hero-grid,
    .content-grid,
    .features-grid,
    .footer-container {
        grid-template-columns: 1fr 1fr;
    }

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

@media (max-width: 768px) {
    html {
        scroll-padding-top: 72px;
    }

    .nav-toggle {
        display: inline-flex;
        align-items: center;
        justify-content: center;
    }

    .nav-menu {
        position: fixed;
        top: 72px;
        left: 20px;
        right: 20px;
        flex-direction: column;
        align-items: stretch;
        padding: 16px;
        border: 1px solid var(--border);
        border-radius: var(--radius-lg);
        background: rgba(255, 255, 255, 0.96);
        box-shadow: var(--shadow-lg);
        opacity: 0;
        visibility: hidden;
        transform: translateY(-12px);
        transition: var(--transition);
    }

    .nav-menu.active {
        opacity: 1;
        visibility: visible;
        transform: translateY(0);
    }

    .nav-link {
        width: 100%;
        justify-content: center;
    }

    .hero-section,
    .content-section,
    .features-section,
    .how-to-section,
    .faq-section {
        padding: 64px 0;
    }

    .hero-section h1 {
        font-size: 2.35rem;
    }

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

    .content-grid,
    .features-grid,
    .footer-container {
        grid-template-columns: 1fr;
    }

    .step {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .step-number {
        margin: 0 auto;
    }
}

@media (max-width: 480px) {
    .container,
    .navbar,
    .footer-container,
    .footer-bottom {
        width: min(100%, calc(100% - 24px));
    }

    .hero-section h1 {
        font-size: 1.95rem;
    }

    .converter-panel,
    .content-card,
    .feature-card,
    .step {
        padding: 20px;
    }

    .hero-highlights {
        gap: 10px;
    }

    .hero-highlights li {
        width: 100%;
        text-align: center;
    }

    .file-info-box {
        flex-wrap: wrap;
    }
}