:root {
    --bg: #eef7ff;
    --bg-soft: #f7fbff;
    --surface: rgba(255, 255, 255, 0.78);
    --surface-strong: #ffffff;
    --primary: #69afe5;
    --primary-deep: #2d6eaa;
    --text: #1e3a52;
    --text-soft: #5f7c93;
    --line: rgba(111, 165, 210, 0.22);
    --shadow: 0 18px 40px rgba(99, 152, 198, 0.16);
}

* {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    margin: 0;
    min-height: 100vh;
    font-family: "Avenir Next", "PingFang SC", "Microsoft YaHei", sans-serif;
    color: var(--text);
    background:
        radial-gradient(circle at top left, rgba(160, 222, 255, 0.54), transparent 30%),
        radial-gradient(circle at top right, rgba(202, 235, 255, 0.82), transparent 26%),
        linear-gradient(180deg, #f7fbff 0%, #eef7ff 48%, #e8f4ff 100%);
}

a {
    color: inherit;
    text-decoration: none;
}

.page-shell {
    width: min(1180px, calc(100% - 32px));
    margin: 0 auto;
}

.site-header {
    position: sticky;
    top: 0;
    z-index: 20;
    backdrop-filter: blur(18px);
    background: rgba(245, 251, 255, 0.8);
    border-bottom: 1px solid rgba(126, 180, 220, 0.18);
}

.nav-wrap {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 18px;
    padding: 18px 0;
}

.brand {
    font-size: 1.08rem;
    font-weight: 700;
    letter-spacing: 0.08em;
    color: var(--primary-deep);
}

.nav-links {
    display: flex;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
}

.nav-links a {
    padding: 10px 16px;
    border-radius: 999px;
    color: var(--text-soft);
    transition: background-color 0.25s ease, transform 0.25s ease, color 0.25s ease;
}

.nav-links a:hover {
    background: rgba(103, 174, 230, 0.12);
    color: var(--primary-deep);
    transform: translateY(-1px);
}

.hero {
    padding: 58px 0 24px;
    text-align: center;
}

.eyebrow {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 8px 16px;
    border-radius: 999px;
    background: rgba(152, 216, 244, 0.18);
    color: var(--primary-deep);
    font-size: 0.95rem;
    font-weight: 600;
}

.hero h1 {
    margin: 22px 0 14px;
    font-size: clamp(2.2rem, 5vw, 4rem);
    line-height: 1.08;
    letter-spacing: -0.04em;
}

.hero p {
    width: min(760px, 100%);
    margin: 0 auto;
    color: var(--text-soft);
    font-size: 1.05rem;
    line-height: 1.9;
}

.content-section {
    padding: 14px 0 46px;
}

.section-card {
    background: var(--surface);
    border: 1px solid var(--line);
    border-radius: 30px;
    box-shadow: var(--shadow);
    backdrop-filter: blur(18px);
}

.media-card {
    padding: 28px;
}

.section-heading {
    display: flex;
    justify-content: space-between;
    gap: 18px;
    align-items: end;
    margin-bottom: 22px;
}

.section-heading h2 {
    margin: 0;
    font-size: clamp(1.6rem, 3.8vw, 2.4rem);
}

.section-heading p {
    margin: 0;
    max-width: 560px;
    line-height: 1.8;
    color: var(--text-soft);
}

.video-panel {
    overflow: hidden;
    border-radius: 24px;
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.92), rgba(231, 245, 255, 0.92));
    border: 1px solid rgba(103, 174, 230, 0.2);
    box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.34);
}

.video-panel iframe,
.video-panel video {
    display: block;
    width: 100%;
    aspect-ratio: 16 / 9;
    background: #d9ebfb;
    border: 0;
}

.ppt-card {
    margin-top: 28px;
    padding: 28px;
}

.viewer-head {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    margin-bottom: 18px;
}

.viewer-head h3 {
    margin: 0;
    font-size: 1.35rem;
}

.viewer-head p {
    margin: 0;
    color: var(--text-soft);
    line-height: 1.8;
}

.ppt-viewer {
    position: relative;
    border-radius: 24px;
    overflow: hidden;
    border: 1px solid rgba(103, 174, 230, 0.2);
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.94), rgba(233, 245, 255, 0.92));
    box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.34);
}

.ppt-frame {
    display: block;
    width: 100%;
    height: min(78vw, 980px);
    border: 0;
    background: #e0effd;
}

.viewer-hint {
    margin-top: 14px;
    color: var(--text-soft);
    font-size: 0.95rem;
    line-height: 1.8;
}

.viewer-hint a {
    color: var(--primary-deep);
    font-weight: 600;
}

.site-footer {
    padding: 12px 0 42px;
    text-align: center;
    color: var(--text-soft);
    font-size: 0.96rem;
}

.site-footer a {
    color: var(--primary-deep);
    font-weight: 600;
}

@media (max-width: 860px) {
    .section-heading,
    .viewer-head {
        flex-direction: column;
        align-items: flex-start;
    }

    .ppt-frame {
        height: 92vw;
    }
}

@media (max-width: 640px) {
    .nav-wrap {
        flex-direction: column;
        align-items: flex-start;
        padding: 14px 0;
    }

    .media-card,
    .ppt-card {
        padding: 20px;
    }

    .ppt-frame {
        height: 112vw;
    }
}