/* --- Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@300;400;500;700&display=swap');
@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@300;400;500;700&display=swap');

/* --- Variables --- */
:root {
    --color-background: #FFFFFF;
    --color-text-dark: #2C3E50;
    --color-text-light: #6c7a89;
    --color-accent: #3498DB;
    --color-primary-dark: #1F618D;
    --color-light-gray: #F8F9FA;
    --color-border: #E0E4E8;
    /* 增加了系统级中文字体后备，确保在各类设备上渲染清晰 */
    --font-primary: 'Roboto', 'Noto Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;

    --space-lg: clamp(40px, 8vw, 80px);
    --space-xl: clamp(60px, 10vw, 120px);
}

/* --- Body & Reset --- */
*,
*::before,
*::after {
    box-sizing: border-box;
}

body {
    font-family: var(--font-primary);
    margin: 0;
    line-height: 1.6;
    color: var(--color-text-dark);
    background-color: var(--color-background);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* --- Layout & Spacing --- */
.container {
    width: 92%;
    max-width: 1200px;
    margin: 0 auto;
}

.padding-y-120 {
    padding-top: var(--space-xl);
    padding-bottom: var(--space-lg);
}

.padding-y-80 {
    padding-top: var(--space-lg);
    padding-bottom: var(--space-lg);
}

.padding-y-40 {
    padding-top: 40px;
    padding-bottom: 40px;
}

.margin-top-40 {
    margin-top: clamp(20px, 4vw, 40px);
}

.margin-top-20 {
    margin-top: 20px;
}

.text-center {
    text-align: center;
}

.text-dark {
    color: var(--color-text-dark);
}

/* --- Grid --- */
.grid-3-col {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 30px;
}

/* --- Typography --- */
.title-main {
    font-size: clamp(1.8rem, 4vw, 3.2rem);
    /* 针对中文稍作微调 */
    font-weight: 700;
    line-height: 1.3;
    margin: 0 0 20px 0;
    color: var(--color-primary-dark);
}

.title-section {
    font-size: clamp(1.5rem, 3vw, 2rem);
    font-weight: 700;
    margin-bottom: 20px;
}

.subtitle {
    font-size: 1.15rem;
    color: var(--color-text-light);
    max-width: 800px;
    margin: 0 auto;
}

/* --- Header & Nav (Desktop) --- */
header.fixed-top {
    position: sticky;
    top: 0;
    width: 100%;
    background-color: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(5px);
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.08);
    z-index: 1000;
    transition: all 0.3s ease;
}

header .container {
    padding: 10px 0;
}

.nav-wrapper {
    display: flex;
    align-items: center;
}

nav {
    display: flex;
    align-items: center;
}

nav a {
    text-decoration: none;
    color: var(--color-text-dark);
    font-weight: 500;
    margin-left: 25px;
    font-size: 1rem;
    transition: color 0.3s ease;
    position: relative;
}

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

nav a::after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    bottom: -4px;
    left: 0;
    background-color: var(--color-accent);
    transition: width 0.3s ease;
}

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

.menu-checkbox,
.menu-btn {
    display: none;
}

/* --- Buttons --- */
.cta-button {
    padding: 12px 28px;
    border-radius: 6px;
    font-weight: 700;
    display: inline-block;
    color: #fff;
    background: var(--color-accent);
    text-decoration: none;
    transition: all 0.3s ease;
    border: 2px solid var(--color-accent);
}

.cta-button:hover {
    background: var(--color-primary-dark);
    border-color: var(--color-primary-dark);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(31, 97, 141, 0.3);
}

.lang-switch-button {
    margin-left: 20px;
    margin-right: 10px;
    padding: 6px 14px;
    border: 1px solid var(--color-border);
    border-radius: 4px;
    font-size: 0.9rem;
    color: var(--color-text-dark);
    text-decoration: none;
    transition: background 0.3s ease;
}

.lang-switch-button:hover {
    background: var(--color-light-gray);
}

/* --- Cards --- */
.cards-vertical-list {
    display: flex;
    flex-direction: column;
    gap: 30px;
}

.card {
    padding: 35px;
    background: var(--color-background);
    border-radius: 8px;
    border-left: 5px solid var(--color-accent);
    border: 1px solid var(--color-border);
    border-left-width: 5px;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.03);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.08);
}

.card h3,
.card h4 {
    margin-top: 0;
    color: var(--color-primary-dark);
}

ul.stats-list,
ul.check-list {
    padding-left: 20px;
    line-height: 1.8;
}

ul.stats-list li,
ul.check-list li {
    margin-bottom: 8px;
}

/* --- Responsive Design (Tablet & Mobile) --- */
@media (max-width: 900px) {
    header .container {
        padding: 10px 0;
    }

    header img {
        height: 60px !important;
    }

    .menu-btn {
        display: block;
        cursor: pointer;
        padding: 20px 0 20px 20px;
        z-index: 1001;
    }

    .navicon {
        background: var(--color-text-dark);
        display: block;
        height: 3px;
        position: relative;
        transition: background .2s ease-out;
        width: 24px;
        border-radius: 2px;
    }

    .navicon:before,
    .navicon:after {
        background: var(--color-text-dark);
        content: '';
        display: block;
        height: 100%;
        position: absolute;
        transition: all .2s ease-out;
        width: 100%;
        border-radius: 2px;
    }

    .navicon:before {
        top: 8px;
    }

    .navicon:after {
        top: -8px;
    }

    .menu-checkbox:checked~.menu-btn .navicon {
        background: transparent;
    }

    .menu-checkbox:checked~.menu-btn .navicon:before {
        transform: rotate(-45deg);
        top: 0;
    }

    .menu-checkbox:checked~.menu-btn .navicon:after {
        transform: rotate(45deg);
        top: 0;
    }

    .nav-wrapper {
        position: absolute;
        top: 100%;
        left: 0;
        width: 100%;
        background-color: var(--color-background);
        box-shadow: 0 10px 15px rgba(0, 0, 0, 0.1);
        flex-direction: column;
        align-items: flex-start;
        padding: 0;
        max-height: 0;
        overflow: hidden;
        transition: max-height 0.3s ease-in-out;
    }

    .menu-checkbox:checked~.nav-wrapper {
        max-height: 400px;
        padding-bottom: 20px;
    }

    nav {
        flex-direction: column;
        width: 100%;
        align-items: flex-start;
    }

    nav a {
        margin: 0;
        padding: 15px 5%;
        width: 100%;
        border-bottom: 1px solid var(--color-light-gray);
        font-size: 1.1rem;
    }

    nav a::after {
        display: none;
    }

    .lang-switch-button {
        margin: 20px 5% 10px 5%;
        width: 90%;
        text-align: center;
    }

    .card {
        padding: 25px 20px;
    }

    img {
        max-width: 100%;
        height: auto;
    }
}

@media (max-width: 600px) {
    header img {
        height: 50px !important;
    }

    .tech-grid {
        grid-template-columns: 1fr !important;
    }
}