/* ===== CSS Variables - Modern International ===== */
:root {
    --primary: #1a365d;
    --primary-light: #2c5282;
    --accent: #3182ce;
    --accent-light: #63b3ed;
    --card-selected: #e53e3e;
    --dark: #1a202c;
    --gray-900: #171923;
    --gray-800: #2d3748;
    --gray-700: #4a5568;
    --gray-600: #718096;
    --gray-500: #a0aec0;
    --gray-400: #cbd5e0;
    --gray-300: #e2e8f0;
    --gray-200: #edf2f7;
    --gray-100: #f7fafc;
    --white: #ffffff;
    --gradient-primary: linear-gradient(135deg, #1a365d 0%, #2c5282 50%, #3182ce 100%);
    --gradient-accent: linear-gradient(135deg, #3182ce 0%, #63b3ed 100%);
    --gradient-hero: linear-gradient(135deg, rgba(26, 54, 93, 0.95) 0%, rgba(44, 82, 130, 0.85) 100%);
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.08);
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 10px 40px rgba(0, 0, 0, 0.12);
    --shadow-xl: 0 20px 60px rgba(0, 0, 0, 0.15);
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
    scroll-behavior: smooth;
    font-size: 16px;
    scroll-padding-top: 100px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'Helvetica Neue', Arial, sans-serif;
    line-height: 1.6;
    color: var(--gray-800);
    background: var(--white);
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 2rem;
    overflow-x: hidden;
}

/* ===== Hero Section ===== */
.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
    overflow: hidden;
    padding: 6rem 2rem 4rem;
    background-image: url('assets/images/hero-bg.png');
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
}

.hero-overlay {
    position: absolute;
    inset: 0;
    background: rgba(17,17,17,0.1);
    z-index: 1;
}

/* ===== Navigation ===== */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(20px);
    box-shadow: var(--shadow-sm);
    transition: var(--transition);
}

.navbar.scrolled {
    box-shadow: var(--shadow);
}

.nav-container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 1.25rem 2rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.nav-logo img {
    height: 80px;
    width: 100%;
}

.logo-text {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary);
    letter-spacing: -0.02em;
}

.nav-links {
    display: flex;
    list-style: none;
    gap: 2.5rem;
}

.nav-link {
    text-decoration: none;
    color: var(--gray-700);
    font-weight: 500;
    font-size: 0.95rem;
    position: relative;
    transition: var(--transition);
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: -6px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--accent);
    transition: var(--transition);
}

.nav-link:hover::after,
.nav-link.active::after {
    width: 100%;
}

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

.nav-actions {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.lang-switcher {
    display: flex;
    gap: 0.5rem;
}

.lang-btn {
    padding: 0.5rem 0.9rem;
    border: 1px solid var(--gray-300);
    background: var(--white);
    color: var(--gray-700);
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 500;
    transition: var(--transition);
}

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

.nav-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
}

.nav-toggle span {
    width: 24px;
    height: 2px;
    background: var(--gray-800);
    transition: var(--transition);
}

.hero-content {
    position: relative;
    z-index: 2;
    text-align: center;
    max-width: 900px;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.6rem 1.5rem;
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: 50px;
    color: var(--white);
    font-size: 0.9rem;
    margin-bottom: 2rem;
}

.badge-dot {
    width: 8px;
    height: 8px;
    background: var(--accent-light);
    border-radius: 50%;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.hero-title {
    margin-bottom: 1.5rem;
}

.title-cn {
    display: block;
    font-size: 4rem;
    font-weight: 800;
    color: var(--white);
    margin-bottom: 0.5rem;
    letter-spacing: -0.02em;
}

.title-en {
    display: block;
    font-size: 2.5rem;
    font-weight: 600;
    color: var(--accent-light);
    letter-spacing: 0.05em;
}

.hero-subtitle {
    font-size: 1.4rem;
    color: rgba(255, 255, 255, 0.9);
    margin-bottom: 1rem;
    font-weight: 400;
}

.hero-desc {
    font-size: 1.1rem;
    color: rgba(255, 255, 255, 0.75);
    margin-bottom: 2.5rem;
    line-height: 1.8;
}

.hero-ctas {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

.btn {
    padding: 1rem 2rem;
    border-radius: 8px;
    font-weight: 600;
    text-decoration: none;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
    border: none;
    font-size: 1rem;
}

.btn-primary {
    background: var(--white);
    color: var(--primary);
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.15);
}

.btn-outline {
    background: transparent;
    color: var(--white);
    border: 2px solid rgba(255, 255, 255, 0.3);
}

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

.btn-lg {
    padding: 1.2rem 2.5rem;
    font-size: 1.05rem;
}

.btn-full {
    width: 100%;
    justify-content: center;
}

.hero-visual {
    position: absolute;
    right: 5%;
    bottom: 10%;
    z-index: 1;
}

.hero-product-img {
    max-width: 300px;
    height: auto;
    filter: drop-shadow(0 20px 40px rgba(0, 0, 0, 0.3));
    animation: float 6s ease-in-out infinite;
}

@keyframes float {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-20px); }
}

.hero-scroll {
    position: absolute;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%);
}

.scroll-indicator {
    width: 30px;
    height: 50px;
    border: 2px solid rgba(255, 255, 255, 0.3);
    border-radius: 15px;
    position: relative;
}

.scroll-indicator span {
    position: absolute;
    top: 8px;
    left: 50%;
    transform: translateX(-50%);
    width: 4px;
    height: 10px;
    background: var(--white);
    border-radius: 2px;
    animation: scrollDown 2s infinite;
}

@keyframes scrollDown {
    0% { opacity: 1; top: 8px; }
    100% { opacity: 0; top: 30px; }
}

/* ===== Section Styles ===== */
section {
    padding: 6rem 0;
}

.section-header {
    text-align: center;
    margin-bottom: 4rem;
}

.section-tag {
    display: inline-block;
    padding: 0.5rem 1.5rem;
    background: var(--accent);
    color: var(--white);
    border-radius: 50px;
    font-size: 0.85rem;
    font-weight: 600;
    margin-bottom: 1rem;
    letter-spacing: 0.05em;
}

.section-title {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--gray-900);
    margin-bottom: 1rem;
    letter-spacing: -0.02em;
}

.section-line {
    width: 60px;
    height: 4px;
    background: var(--gradient-accent);
    margin: 1.5rem auto;
    border-radius: 2px;
}

.section-desc {
    font-size: 1.1rem;
    color: var(--gray-600);
    max-width: 600px;
    margin: 0 auto;
}

/* ===== About Section ===== */
.about {
    background: var(--white);
}

.about-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    align-items: center;
}

.about-text p {
    text-align: justify;
    color: var(--gray-700);
    margin-bottom: 1.5rem;
    line-height: 1.8;
}

body.lang-en .about-text p {
    text-align: left !important;
}

.about-intro {
    font-size: 1.1rem;
}

.about-philosophy {
    font-size: 1rem;
}

.about-visual {
    position: relative;
}

.about-card {
    position: relative;
    padding: 2rem;
    background: var(--gradient-primary);
    border-radius: 20px;
    overflow: hidden;
    color: var(--white);
}

.about-card-bg {
    position: absolute;
    inset: 0;
    background: 
        radial-gradient(circle at 30% 30%, rgba(255, 255, 255, 0.1) 0%, transparent 50%),
        radial-gradient(circle at 70% 70%, rgba(255, 255, 255, 0.05) 0%, transparent 50%);
}

.about-card-content {
    position: relative;
    z-index: 1;
}

.about-card h3 {
    color: #15cf6c;
    font-size: 1.3rem;
    margin-bottom: 1rem;
    font-weight: 700;
}

.about-card p {
    color: rgba(255, 255, 255, 0.85);
    text-align: justify;
    margin-bottom: 1rem;
    line-height: 1.8;
}

body.lang-en .about-card p {
    text-align: left !important;
}

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

.stat {
    text-align: center;
    padding: 1rem;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 12px;
    backdrop-filter: blur(10px);
}

.stat-number {
    display: block;
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--white);
}

.stat-label {
    font-size: 0.9rem;
    color: rgba(255, 255, 255, 0.75);
}

/* ===== Products Section ===== */
.products {
    background: var(--gray-100);
}

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

.product-card {
    background: var(--white);
    border-radius: 16px;
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: var(--transition);
    position: relative;
    border: 1.5px solid var(--accent);
    min-width: 0;
    overflow-wrap: break-word;
    cursor: pointer;
}

.product-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-xl);
    border-color: var(--card-selected);
}

.product-card.active {
    border-color: var(--card-selected);
    box-shadow: var(--shadow-xl);
}

.other-product-card[href="product-m6.html"] { border-left: 4px solid var(--accent); }
.other-product-card[href="product-m9.html"] { border-left: 4px solid #e7bd00f6; }
.other-product-card[href="product-m2-1.html"] { border-left: 4px solid #e53e3e; }
.other-product-card[href="product-m3.html"] { border-left: 4px solid #38a169; }

.product-badge {
    position: absolute;
    top: 1rem;
    right: 1rem;
    padding: 0.5rem 1rem;
    border-radius: 50px;
    font-size: 0.8rem;
    font-weight: 600;
    z-index: 2;
}

.product-badge-new {
    background: var(--accent);
    color: var(--white);
}

.product-badge-featured {
    background: #e7bd00f6;
    color: var(--white);
}

.product-badge-alloy {
    background: #e53e3e;
    color: var(--white);
}

.product-badge-mineral {
    background: #38a169;
    color: var(--white);
}

.product-image {
    height: 280px;
    background: var(--gray-100);
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
}

.product-image img {
    max-width: 80%;
    max-height: 80%;
    object-fit: contain;
    transition: var(--transition);
}

.product-card:hover .product-image img {
    transform: scale(1.08);
}

.product-info {
    padding: 2rem;
}

.product-name {
    font-size: 1.8rem;
    font-weight: 800;
    color: var(--gray-900);
    margin-bottom: 0.5rem;
    letter-spacing: -0.02em;
}

.product-subtitle {
    font-size: 1rem;
    color: var(--accent);
    font-weight: 600;
    margin-bottom: 1rem;
}

.product-desc {
    color: var(--gray-700);
    line-height: 1.7;
    margin-bottom: 1.5rem;
    overflow-wrap: break-word;
}

.product-features {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
}

.feature-tag {
    padding: 0.4rem 0.8rem;
    background: var(--gray-100);
    color: var(--gray-700);
    border-radius: 50px;
    font-size: 0.85rem;
    font-weight: 500;
    border: 1px solid var(--gray-300);
}

.product-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--accent);
    text-decoration: none;
    font-weight: 600;
    transition: var(--transition);
}

.product-link:hover {
    gap: 1rem;
    color: var(--primary);
}

/* ===== Scenarios Section ===== */
.scenarios {
    background: var(--white);
}

.scenarios-grid {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 2rem;
}

.scenario-card {
    text-align: center;
    padding: 2rem;
    background: var(--white);
    border-radius: 16px;
    box-shadow: var(--shadow);
    transition: var(--transition);
    border: 1px solid var(--gray-200);
    min-width: 0;
    overflow-wrap: break-word;
}

.scenario-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-lg);
    border-color: var(--accent);
}

.scenario-icon {
    width: 80px;
    height: 80px;
    margin: 0 auto 1rem;
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    position: relative;
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.25), inset 0 -1px 2px rgba(0, 0, 0, 0.2), 0 4px 10px rgba(0, 0, 0, 0.15);
}
.scenario-icon::after {
    content: '';
    position: absolute;
    inset: 0;
    border-radius: 16px;
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.2) 0%, rgba(255, 255, 255, 0) 40%, rgba(0, 0, 0, 0.12) 100%);
    pointer-events: none;
}

.scenarios-grid .scenario-card:nth-child(1) .scenario-icon { background: linear-gradient(135deg, #60a5fa 0%, #2563eb 50%, #1e3a8a 100%); }
.scenarios-grid .scenario-card:nth-child(2) .scenario-icon { background: linear-gradient(135deg, #2dd4bf 0%, #0d9488 50%, #134e4a 100%); }
.scenarios-grid .scenario-card:nth-child(3) .scenario-icon { background: linear-gradient(135deg, #fb923c 0%, #ea580c 50%, #7c2d12 100%); }
.scenarios-grid .scenario-card:nth-child(4) .scenario-icon { background: linear-gradient(135deg, #818cf8 0%, #4f46e5 50%, #1e1b4b 100%); }
.scenarios-grid .scenario-card:nth-child(5) .scenario-icon { background: linear-gradient(135deg, #34d399 0%, #059669 50%, #064e3b 100%); }
.scenarios-grid .scenario-card:nth-child(6) .scenario-icon { background: linear-gradient(135deg, #c084fc 0%, #7c3aed 50%, #3b0764 100%); }
.scenarios-grid .scenario-card:nth-child(7) .scenario-icon { background: linear-gradient(135deg, #fb7185 0%, #e11d48 50%, #881337 100%); }
.scenarios-grid .scenario-card:nth-child(8) .scenario-icon { background: linear-gradient(135deg, #f87171 0%, #dc2626 50%, #7f1d1d 100%); }

.scenario-card:hover .scenario-icon {
    transform: scale(1.08);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
}

.scenario-icon svg {
    width: 40px;
    height: 40px;
    color: var(--white);
}

.scenario-card h4 {
    font-size: 1.1rem;
    color: var(--gray-900);
    font-weight: 600;
    overflow-wrap: break-word;
}

/* ===== Advantages Section ===== */
.advantages {
    background: var(--gray-100);
}

.advantages-grid {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 2rem;
}

.advantage-card {
    text-align: center;
    padding: 2.5rem 1.5rem;
    background: var(--white);
    border-radius: 16px;
    box-shadow: var(--shadow);
    transition: var(--transition);
    position: relative;
    border: 1px solid var(--gray-200);
    min-width: 0;
    overflow-wrap: break-word;
}

.advantage-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-lg);
    border-color: var(--accent);
}

.advantage-number {
    position: absolute;
    top: 1rem;
    right: 1rem;
    font-size: 3rem;
    font-weight: 900;
    color: var(--gray-200);
    line-height: 1;
}

.advantage-icon {
    width: 70px;
    height: 70px;
    margin: 0 auto 1.5rem;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.advantages-grid .advantage-card:nth-child(1) .advantage-icon { background: linear-gradient(135deg, #3182ce, #2b6cb0); box-shadow: 0 4px 14px rgba(49, 130, 206, 0.35); }
.advantages-grid .advantage-card:nth-child(2) .advantage-icon { background: linear-gradient(135deg, #10b981, #059669); box-shadow: 0 4px 14px rgba(16, 185, 129, 0.35); }
.advantages-grid .advantage-card:nth-child(3) .advantage-icon { background: linear-gradient(135deg, #f59e0b, #d97706); box-shadow: 0 4px 14px rgba(245, 158, 11, 0.35); }
.advantages-grid .advantage-card:nth-child(4) .advantage-icon { background: linear-gradient(135deg, #8b5cf6, #7c3aed); box-shadow: 0 4px 14px rgba(139, 92, 246, 0.35); }

.advantage-card:hover .advantage-icon {
    transform: scale(1.1);
}

.advantage-icon svg {
    width: 35px;
    height: 35px;
    color: var(--white);
}

.advantage-card h4 {
    font-size: 1.3rem;
    color: var(--gray-900);
    margin-bottom: 1rem;
    font-weight: 700;
}

.advantage-card p {
    color: var(--gray-700);
    line-height: 1.7;
    overflow-wrap: break-word;
}

/* ===== CTA Banner ===== */
.cta-banner {
    position: relative;
    padding: 6rem 0;
    background: var(--gradient-primary);
    overflow: hidden;
}

.cta-overlay {
    position: absolute;
    inset: 0;
    background: 
        radial-gradient(circle at 20% 50%, rgba(255, 255, 255, 0.05) 0%, transparent 50%),
        radial-gradient(circle at 80% 50%, rgba(255, 255, 255, 0.03) 0%, transparent 50%);
}

.cta-content {
    position: relative;
    z-index: 1;
    text-align: center;
    color: var(--white);
}

.cta-content h2 {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: 1rem;
    line-height: 1.4;
}

.cta-content p {
    font-size: 1.2rem;
    color: rgba(255, 255, 255, 0.85);
    margin-bottom: 2rem;
}

/* ===== Contact Section ===== */
.contact {
    background: var(--white);
}

.contact-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
}

.contact-info {
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

.contact-item {
    display: flex;
    align-items: flex-start;
    gap: 1rem;
}

.contact-icon {
    width: 50px;
    height: 50px;
    background: var(--gradient-primary);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.contact-icon svg {
    width: 24px;
    height: 24px;
    color: var(--white);
}

.contact-item h4 {
    font-size: 1.1rem;
    color: var(--gray-900);
    margin-bottom: 0.25rem;
}

.contact-item p {
    color: var(--gray-700);
}

.contact-form-wrapper {
    background: var(--white);
    padding: 2.5rem;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--gray-200);
}

.contact-form {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.form-group {
    position: relative;
}

.form-input {
    width: 100%;
    padding: 1rem 1.2rem;
    border: 2px solid var(--gray-300);
    border-radius: 8px;
    font-size: 1rem;
    font-family: inherit;
    transition: var(--transition);
    background: var(--white);
    color: var(--gray-900);
}

.form-input:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 4px rgba(49, 130, 206, 0.1);
}

textarea.form-input {
    resize: vertical;
    min-height: 120px;
}

/* ===== Footer ===== */
.footer {
    background: var(--gray-900);
    color: var(--white);
    padding: 4rem 0 2rem;
}

.footer-grid {
    display: grid;
    grid-template-columns: minmax(0, 2fr) minmax(0, 1fr);
    gap: 3rem;
    margin-bottom: 3rem;
}

.footer-brand {
    min-width: 0;
    overflow-wrap: break-word;
}

.footer-right {
    display: flex;
    justify-content: flex-end;
    gap: 3rem;
    min-width: 0;
}

.footer-right .footer-links {
    text-align: right;
    min-width: 0;
    overflow-wrap: break-word;
}

.footer-right .footer-links ul {
    list-style: none;
    padding: 0;
}

.footer-right .footer-links ul li {
    margin-bottom: 0.5rem;
    white-space: nowrap;
}

.footer-brand .footer-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-bottom: 1rem;
}

.footer-brand .footer-logo img {
    height: 60px;
}

.footer-brand .footer-logo span {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--white);
}

.footer-brand p {
    color: var(--gray-500);
    margin-bottom: 0.5rem;
}

.footer-slogan {
    font-style: italic;
    color: var(--accent-light);
}

.footer-links h4 {
    font-size: 1rem;
    margin-bottom: 1.5rem;
    color: var(--white);
    font-weight: 600;
}

.footer-links ul {
    list-style: none;
}

.footer-links li {
    margin-bottom: 0.75rem;
}

.footer-links a {
    color: var(--gray-500);
    text-decoration: none;
    transition: var(--transition);
}

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

.footer-links li {
    color: var(--gray-500);
}

.footer-bottom {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid var(--gray-800);
    color: var(--gray-600);
}

/* ===== Back to Top ===== */
.back-to-top {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    background: var(--accent);
    border: none;
    border-radius: 50%;
    color: var(--white);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition);
    z-index: 999;
    box-shadow: var(--shadow-lg);
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}

.back-to-top:hover {
    transform: translateY(-5px);
    background: var(--primary);
}

.back-to-top svg {
    width: 24px;
    height: 24px;
}

/* ===== Responsive Design ===== */
@media (max-width: 1024px) {
    .about-grid,
    .contact-grid {
        grid-template-columns: 1fr;
        gap: 3rem;
    }

    .products-grid,
    .advantages-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

    .scenarios-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

    .footer-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

    .nav-links {
        gap: 1.2rem;
    }

    .nav-link {
        font-size: 0.85rem;
    }

    .nav-logo img {
        height: 80px;
    }

    .logo-text {
        font-size: 1.2rem;
    }
}

@media (max-width: 768px) {
    .nav-container {
        padding: 0.75rem 1rem;
    }

    .nav-logo img {
        height: 48px;
    }

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

    .nav-links {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--white);
        flex-direction: column;
        padding: 2rem;
        box-shadow: var(--shadow-lg);
    }

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

    .nav-toggle {
        display: flex;
    }

    .nav-actions {
        display: flex;
        align-items: center;
        gap: 0.75rem;
        flex-shrink: 0;
    }

    .lang-switcher {
        display: flex;
        gap: 0.4rem;
    }

    .lang-btn {
        padding: 0.4rem 0.7rem;
        font-size: 0.8rem;
    }

    .hero-title .title-cn {
        font-size: 2.5rem;
    }

    .hero-title .title-en {
        font-size: 1.8rem;
    }

    .hero-subtitle {
        font-size: 1.2rem;
    }

    .hero-visual {
        display: none;
    }

    .form-input {
        padding: 0.65rem 0.8rem;
        font-size: 14px;
    }

    select.form-input {
        font-size: 14px;
        -webkit-appearance: menulist;
        appearance: menulist;
    }

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

    .products-grid,
    .advantages-grid {
        grid-template-columns: 1fr;
    }

    .scenarios-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

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

    .footer-right {
        justify-content: flex-start;
        flex-wrap: wrap;
        gap: 2rem;
    }

    .footer-right .footer-links {
        text-align: left;
    }

    .cta-content h2 {
        font-size: 1.8rem;
    }

    /* 移动端文字对齐修复 */
    .about-text p {
        text-align: justify;
    }

    body.lang-en .about-text p {
        text-align: left !important;
    }

    .about-card p {
        text-align: justify;
    }

    body.lang-en .about-card p {
        text-align: left !important;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 1rem;
        overflow-x: hidden;
    }

    .hero {
        padding: 5rem 1rem 3rem;
    }

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

    .hero-title .title-en {
        font-size: 1.5rem;
    }

    .btn {
        padding: 0.8rem 1.5rem;
        font-size: 0.9rem;
    }

    .about-stats {
        grid-template-columns: 1fr;
    }

    .scenarios-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
        gap: 1rem;
    }

    .scenario-card {
        padding: 1.2rem 0.8rem;
        overflow: hidden;
    }

    .scenario-card h4 {
        font-size: 0.85rem;
        word-break: break-word;
    }

    .scenario-icon {
        width: 56px;
        height: 56px;
    }

    /* 移动端文字对齐修复 */
    .about-text p {
        text-align: justify;
    }

    body.lang-en .about-text p {
        text-align: left !important;
    }

    .about-card p {
        text-align: justify;
    }

    body.lang-en .about-card p {
        text-align: left !important;
    }
}