:root {
    --header-height: 5rem;
    --primary-color: #2563eb;
    --primary-dark: #1d4ed8;
    --primary-light: #3b82f6;
    --secondary-color: #10b981;
    --text-color: #1f2937;
    --text-light: #6b7280;
    --bg-color: #ffffff;
    --bg-secondary: #f3f4f6;
    --border-color: #e5e7eb;
    --shadow: 0 2px 8px 0 rgb(0 0 0 / 0.1);
    --transition: all 0.3s ease;
    --radius: 8px;
    --radius-lg: 16px;
    
    /* SEO优化：焦点可见性颜色 */
    --focus-color: var(--primary-color);
    --focus-offset: 2px;
}

*
{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    
    /* 性能优化：优化渲染性能 */
    -webkit-text-size-adjust: 100%;
    -moz-text-size-adjust: 100%;
    text-size-adjust: 100%;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Microsoft YaHei', sans-serif;
    font-size: 16px;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    
    /* 可访问性：优化文本渲染 */
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
}
h1, h2, h3, h4 {
    font-weight: 600;
    line-height: 1.3;
}
a {
    text-decoration: none;
    color: inherit;
    
    /* SEO/可访问性：改善焦点可见性 */
    &:focus-visible {
        outline: 2px solid var(--focus-color);
        outline-offset: var(--focus-offset);
        border-radius: 2px;
    }
}

/* SEO优化：键盘导航焦点样式 */
:focus-visible {
    outline: 2px solid var(--focus-color);
    outline-offset: var(--focus-offset);
}

/* 移除默认焦点样式（仅对鼠标用户） */
:focus:not(:focus-visible) {
    outline: none;
}

ul {
    list-style: none;
}
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}
.section {
    padding: 5rem 0;
}
.section__title {
    font-size: 2.5rem;
    text-align: center;
    margin-bottom: 0.5rem;
    color: var(--primary-color);
}
.section__subtitle {
    text-align: center;
    color: var(--text-light);
    font-size: 1.1rem;
    margin-bottom: 3rem;
}
.button {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.875rem 2rem;
    border-radius: var(--radius);
    font-weight: 500;
    font-size: 1rem;
    cursor: pointer;
    transition: var(--transition);
    border: 2px solid transparent;
}
.button--primary {
    background: var(--primary-color);
    color: white;
}
.button--primary:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}
.button--outline {
    background: transparent;
    border-color: var(--primary-color);
    color: var(--primary-color);
}
.button--outline:hover {
    background: var(--primary-color);
    color: white;
}
.button--full {
    width: 100%;
}
.header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    z-index: 1000;
    box-shadow: var(--shadow);
    transition: var(--transition);
}
.header.scroll-header {
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}
.nav {
    height: var(--header-height);
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.nav__logo {
    display: flex;
    flex-direction: column;
}
.nav__logo h1 {
    font-size: 1.5rem;
    color: var(--primary-color);
    font-weight: 700;
}
.nav__subtitle {
    font-size: 0.75rem;
    color: var(--text-light);
}
.nav__menu {
    display: flex;
    gap: 2rem;
}
.nav__list {
    display: flex;
    gap: 2rem;
}
.nav__link {
    font-weight: 500;
    color: var(--text-color);
    position: relative;
    padding: 0.5rem 0;
    transition: var(--transition);
}
.nav__link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--primary-color);
    transition: var(--transition);
}
.nav__link:hover,
.nav__link.active {
    color: var(--primary-color);
}
.nav__link:hover::after,
.nav__link.active::after {
    width: 100%;
}
.nav__toggle,
.nav__close {
    display: none;
    cursor: pointer;
    color: var(--text-color);
}
.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    background: linear-gradient(135deg, #f3f4f6 0%, #e5e7eb 100%);
    padding-top: var(--header-height);
}
.hero__container {
    display: grid;
    grid-template-columns: 1fr;
    gap: 4rem;
    align-items: center;
}
.hero__content {
    z-index: 1;
}
.hero__title {
    margin-bottom: 1.5rem;
}
.hero__title-small {
    display: block;
    font-size: 1rem;
    color: var(--text-light);
    margin-bottom: 0.5rem;
    font-weight: 400;
}
.hero__title-main {
    display: block;
    font-size: 3.5rem;
    color: var(--primary-color);
    font-weight: 700;
    line-height: 1.1;
    margin-bottom: 0.25rem;
}
.hero__title-sub {
    display: block;
    font-size: 1.25rem;
    color: var(--text-light);
    font-weight: 400;
}
.hero__description {
    font-size: 1.125rem;
    color: var(--text-light);
    margin-bottom: 2rem;
    line-height: 1.8;
}
.hero__buttons {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}
.about {
    background: var(--bg-secondary);
}
.about__content {
    display: grid;
    gap: 3rem;
}
.about__description {
    font-size: 1.125rem;
    color: var(--text-light);
    margin-bottom: 2rem;
    line-height: 1.8;
}
.about__stats {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    padding: 2rem;
    background: var(--bg-color);
    border-radius: var(--radius-lg);
    text-align: center;
}
.stat__item {
    text-align: center;
}
.stat__number {
    display: block;
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--primary-color);
}
.stat__text {
    display: block;
    color: var(--text-light);
    font-size: 0.875rem;
    margin-top: 0.5rem;
}
.about__features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
}
.feature__card {
    padding: 2rem;
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    transition: var(--transition);
}
.feature__card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    border-color: var(--primary-color);
}
.feature__icon {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}
.feature__title {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    color: var(--text-color);
}
.feature__description {
    color: var(--text-light);
    font-size: 0.9rem;
}
.services {
    background: var(--bg-color);
}
.services__grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2rem;
}
.service__card {
    background: var(--bg-color);
    padding: 2rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow);
    transition: var(--transition);
    border: 1px solid var(--border-color);
}
.service__card:hover {
    transform: translateY(-10px);
    box-shadow: var(--shadow);
    border-color: var(--primary-color);
}
.service__icon {
    font-size: 3rem;
    margin-bottom: 1.5rem;
}
.service__title {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: var(--text-color);
}
.service__description {
    color: var(--text-light);
    margin-bottom: 1.5rem;
    line-height: 1.6;
}
.service__list {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}
.service__list li {
    position: relative;
    padding-left: 1.5rem;
    color: var(--text-light);
    font-size: 0.9rem;
}
.service__list li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--secondary-color);
    font-weight: bold;
}
.contact {
    background: var(--bg-secondary);
}
.contact__content {
    display: grid;
    grid-template-columns: 1fr 1.5fr;
    gap: 4rem;
    align-items: start;
}
.contact__title {
    font-size: 1.5rem;
    margin-bottom: 2rem;
    color: var(--text-color);
}
.contact__item {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    align-items: flex-start;
}
.contact__icon {
    flex-shrink: 0;
    width: 48px;
    height: 48px;
    background: var(--primary-color);
    border-radius: var(--radius);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
}
.contact__item h4 {
    font-size: 1rem;
    margin-bottom: 0.25rem;
    color: var(--text-color);
}
.contact__item p {
    color: var(--text-light);
    font-size: 0.9rem;
}
.contact__form-wrapper {
    background: var(--bg-color);
    padding: 2.5rem;
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-color);
}
.form__group {
    margin-bottom: 1.5rem;
}
.form__label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--text-color);
}
.form__input,
.form__textarea {
    width: 100%;
    padding: 0.875rem 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 1rem;
    font-family: inherit;
    transition: var(--transition);
}
.form__input:focus,
.form__textarea:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}
.form__textarea {
    resize: vertical;
    min-height: 120px;
}
.footer {
    background: #1f2937;
    color: white;
    padding-top: 4rem;
}
.footer__content {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: 4rem;
    padding-bottom: 3rem;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}
.footer__info {
    flex: 1;
}
.footer__logo {
    font-size: 1.5rem;
    color: white;
    margin-bottom: 1rem;
}
.footer__description {
    color: rgba(255, 255, 255, 0.7);
    line-height: 1.8;
}
.footer__links h4,
.footer__services h4 {
    font-size: 1.1rem;
    margin-bottom: 1.5rem;
    color: white;
}
.footer__links ul li,
.footer__services ul li {
    margin-bottom: 0.75rem;
}
.footer__links ul li a {
    color: rgba(255, 255, 255, 0.7);
    transition: var(--transition);
}
.footer__links ul li a:hover {
    color: var(--primary-light);
    padding-left: 0.5rem;
}
.footer__services ul li {
    color: rgba(255, 255, 255, 0.7);
}
.footer__bottom {
    text-align: center;
    padding: 2rem 0;
    color: rgba(255, 255, 255, 0.5);
    font-size: 0.875rem;
}
.footer__bottom p:first-child {
    margin-bottom: 0.5rem;
}
.footer__bottom p:not(:first-child) {
    margin-top: 0.5rem;
}
.footer__icp a {
    color: rgba(255, 255, 255, 0.5);
    transition: var(--transition);
}
.footer__icp a:hover {
    color: var(--primary-light);
}
.scrolltop {
    position: fixed;
    right: 2rem;
    bottom: 2rem;
    width: 48px;
    height: 48px;
    background: var(--primary-color);
    color: white;
    border-radius: var(--radius);
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow);
    opacity: 0;
    visibility: hidden;
    transition: var(--transition);
    z-index: 999;
}
.scrolltop:hover {
    background: var(--primary-dark);
    transform: translateY(-5px);
}
.scrolltop.show {
    opacity: 1;
    visibility: visible;
}
@media screen and (max-width: 1024px) {
    .hero__container {
        grid-template-columns: 1fr;
        text-align: center;
    }
    .contact__content {
        grid-template-columns: 1fr;
    }
    .footer__content {
        grid-template-columns: 1fr 1fr;
    }
}
@media screen and (max-width: 768px) {
    .nav__menu {
        position: fixed;
        top: 0;
        right: -100%;
        width: 80%;
        max-width: 300px;
        height: 100vh;
        background: var(--bg-color);
        box-shadow: var(--shadow);
        padding: 4rem 2rem;
        transition: var(--transition);
        z-index: 1001;
    }
    .nav__menu.show-menu {
        right: 0;
    }
    .nav__list {
        flex-direction: column;
        gap: 1.5rem;
    }
    .nav__close {
        display: block;
        position: absolute;
        top: 1rem;
        right: 1rem;
    }
    .nav__toggle {
        display: block;
    }
    .section {
        padding: 3rem 0;
    }
    .section__title {
        font-size: 2rem;
    }
    .hero__title-main {
        font-size: 2.5rem;
    }
    .about__stats {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
    .footer__content {
        grid-template-columns: 1fr;
        gap: 2rem;
    }
}
@media screen and (max-width: 480px) {
    .container {
        padding: 0 1rem;
    }
    .hero__title-main {
        font-size: 2rem;
    }
    .hero__buttons {
        flex-direction: column;
    }
    .button {
        width: 100%;
    }
    .services__grid {
        grid-template-columns: 1fr;
    }
}

/* ==================== SEO优化：可访问性与性能增强 ==================== */

/* 减少动画（为有前庭功能障碍的用户） */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
    
    html {
        scroll-behavior: auto;
    }
}

/* 高对比度模式支持 */
@media (prefers-contrast: high) {
    :root {
        --primary-color: #0000cc;
        --text-color: #000000;
        --border-color: #000000;
    }
    
    .button--outline {
        border-width: 3px;
    }
}

/* 打印样式优化（有利于SEO和用户体验） */
@media print {
    *,
    *::before,
    *::after {
        background: transparent !important;
        color: black !important;
        box-shadow: none !important;
        text-shadow: none !important;
    }
    
    header,
    footer,
    .scrolltop,
    .nav__toggle,
    .nav__close,
    .contact__form-wrapper,
    button {
        display: none !important;
    }
    
    a,
    a:visited {
        text-decoration: underline;
    }
    
    a[href]::after {
        content: " (" attr(href) ")";
    }
    
    body {
        font-size: 12pt;
        line-height: 1.5;
    }
    
    h1, h2, h3, h4 {
        page-break-after: avoid;
    }
    
    p, h2, h3 {
        orphans: 3;
        widows: 3;
    }
    
    section {
        page-break-inside: avoid;
    }
    
    .container {
        max-width: 100%;
        padding: 0;
    }
    
    .hero {
        min-height: auto;
        padding-top: 0;
    }
    
    .section {
        padding: 1rem 0;
    }
}

/* 深色模式支持（可选） */
@media (prefers-color-scheme: dark) {
    :root {
        --bg-color: #1a1a1a;
        --bg-secondary: #2d2d2d;
        --text-color: #f5f5f5;
        --text-light: #b0b0b0;
        --border-color: #404040;
        --shadow: 0 2px 8px 0 rgb(0 0 0 / 0.4);
    }
    
    .header {
        background: rgba(26, 26, 26, 0.95);
    }
    
    .nav__menu {
        background: var(--bg-color);
    }
    
    .about__stats,
    .feature__card,
    .service__card,
    .contact__form-wrapper {
        background: var(--bg-secondary);
        border-color: var(--border-color);
    }
    
    .footer {
        background: #0a0a0a;
    }
}

/* 跳转链接（提升键盘导航体验） */
.skip-link {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--primary-color);
    color: white;
    padding: 8px;
    text-decoration: none;
    z-index: 100;
}

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

/* 图片懒加载占位符优化 */
img[loading="lazy"] {
    background-color: var(--bg-secondary);
}