/* Yuyi Design System Refined
   Style: Airy, Pastel Gradient, Cyan/Pink/White, Heavily Rounded */

:root {
    /* YuyiColors from Flutter Code */
    --primary-blue: #2E86DE;
    /* Main Brand Blue */
    --primary-teal: #08D9D6;
    /* Second Primary */
    --accent-red: #FF4757;
    /* Accent Red */

    /* Backgrounds */
    --bg-primary: #F8F9FA;
    --bg-white: #FFFFFF;

    /* Text */
    --text-main: #252A34;
    /* Dark Grey */
    --text-sub: #636E72;
    --text-hint: #B2BEC3;

    /* Decorations */
    --shadow-soft: 0 10px 30px -10px rgba(8, 217, 214, 0.15);
    --shadow-card: 0 8px 24px -6px rgba(46, 134, 222, 0.06);

    /* Radius */
    --radius-card: 24px;
    /* YuyiRadius.card */
    --radius-btn: 20px;
    /* YuyiRadius.control */
    --radius-pill: 32px;
    /* YuyiRadius.pill */

    /* Fonts */
    --font-main: "PingFang SC", "Noto Sans SC", ui-sans-serif, system-ui, -apple-system, sans-serif;
    /* Hero 英文主标题使用 Inter，目的是统一 Web/多平台字形观感 */
    --font-hero-en: "Inter", "SF Pro Display", "Helvetica Neue", "Segoe UI", sans-serif;
}

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

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

body {
    /* Lighter Gradient: Teal 20% -> Red 20% over Light BG */
    background: linear-gradient(135deg, rgba(8, 217, 214, 0.12) 0%, rgba(255, 71, 87, 0.12) 100%);
    background-color: var(--bg-primary);
    background-attachment: fixed;
    color: var(--text-main);
    font-family: var(--font-main);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    min-height: 100vh;
}

h1,
h2,
h3 {
    color: var(--text-main);
    font-weight: 800;
    letter-spacing: -0.03em;
}

h1 {
    font-size: clamp(2.5rem, 5vw, 4rem);
    line-height: 1.1;
    margin-bottom: 1.5rem;
}

/* Hero 这句英文是页面第一视觉锚点，单独控制字号和字重，保证“轻但有力量”的观感 */
.hero-title {
    font-family: var(--font-hero-en);
    font-size: clamp(2rem, 4.3vw, 3.4rem);
    font-weight: 400;
    line-height: 1.18;
    letter-spacing: -0.02em;
    max-width: 16ch;
    text-wrap: balance;
}

/* 拆成两行是为了按语义区分轻重：上句更轻，下句更稳 */
.hero-title-line {
    display: block;
}

/* Lightweight by design. -> Inter Regular */
.hero-title-line-soft {
    font-weight: 400;
}

/* Serious by nature. -> Inter Medium / Semibold */
.hero-title-line-strong {
    font-weight: 600;
}

h2 {
    font-size: clamp(1.8rem, 4vw, 2.5rem);
    margin-bottom: 2rem;
}

p {
    color: var(--text-sub);
    font-weight: 500;
    font-size: 1.05rem;
}

/* Utilities */
.container {
    width: 90%;
    max-width: 1200px;
    margin: 0 auto;
    position: relative;
    z-index: 2;
}

.section-padding {
    padding: 6rem 0;
}

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

.grid-2-col {
    display: grid;
    grid-template-columns: 1fr;
    gap: 3rem;
    align-items: center;
}

@media(min-width: 768px) {
    .grid-2-col {
        grid-template-columns: 1fr 1fr;
    }
}

@media(max-width: 767px) {
    /* 移动端可视宽度更窄，进一步收敛字号和行高，避免标题压住下面的功能入口按钮 */
    .hero-title {
        font-size: clamp(1.8rem, 9vw, 2.35rem);
        line-height: 1.22;
    }
}

/* Nav */
.sticky-nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    padding: 1rem 0;
    background: rgba(255, 255, 255, 0.7);
    backdrop-filter: blur(20px);
    z-index: 1000;
}

.nav-inner {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.4rem;
    font-weight: 900;
    color: var(--text-main);
    text-decoration: none;
}

.nav-links {
    display: none;
    gap: 2rem;
    align-items: center;
}

.nav-links a {
    color: var(--text-main);
    font-weight: 600;
    text-decoration: none;
}

/* Nav links hover */
.nav-links a:hover {
    color: var(--primary-blue);
}

@media(min-width: 768px) {
    .nav-links {
        display: flex;
    }
}

/* Buttons */
.btn {
    padding: 14px 28px;
    border-radius: var(--radius-pill);
    font-weight: 700;
    border: none;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    display: inline-flex;
    align-items: center;
    gap: 8px;
    font-size: 1rem;
}

.btn:hover {
    transform: translateY(-3px);
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.1);
}

.btn-cyan {
    background: var(--primary-teal);
    color: #fff;
    box-shadow: 0 8px 20px -4px rgba(8, 217, 214, 0.4);
}

.btn-pink {
    background: var(--accent-red);
    color: #fff;
    box-shadow: 0 8px 20px -4px rgba(255, 71, 87, 0.4);
}

.btn-white {
    background: #fff;
    color: var(--text-main);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.05);
}

/* Hero */
.hero-section {
    min-height: 100vh;
    display: flex;
    align-items: center;
    padding-top: 80px;
    position: relative;
}

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

@media(min-width: 900px) {
    .hero-grid {
        grid-template-columns: 1.1fr 0.9fr;
    }
}

.hero-visual {
    display: flex;
    justify-content: center;
    position: relative;
    perspective: 1000px;
    /* Enable 3D space */
}

.hero-img {
    width: 100%;
    max-width: 420px;
    filter: drop-shadow(0 30px 60px rgba(8, 217, 214, 0.2));
    animation: float 8s ease-in-out infinite;
}

@keyframes float {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-20px);
    }
}

/* Feature Cards */
.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2.5rem;
}

.feature-card {
    background: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(10px);
    border-radius: var(--radius-card);
    padding: 2.5rem;
    box-shadow: var(--shadow-card);
    transition: all 0.3s ease;
    border: 1px solid rgba(255, 255, 255, 0.6);
}

.feature-card:hover {
    transform: translateY(-10px);
    background: #fff;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.08);
}

.feature-icon-img {
    width: 72px;
    height: 72px;
    object-fit: contain;
    margin-bottom: 1.5rem;
}

/* 场景卡片单独做一层视觉语言，原因是这一组卡片承担“代入感”任务，
   如果和功能卡片长得完全一样，用户会把它当成重复信息直接略过。 */
#scenes .scenes-grid {
    gap: 1.8rem;
}

#scenes .scene-card {
    position: relative;
    overflow: hidden;
    padding: 2rem;
    border: 1px solid rgba(8, 217, 214, 0.16);
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.96), rgba(255, 255, 255, 0.88));
    box-shadow: 0 12px 28px -14px rgba(37, 42, 52, 0.28);
}

/* 顶部细色带不是装饰噪音，而是用来强调“这是一个具体场景入口” */
#scenes .scene-card::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 4px;
    background: linear-gradient(90deg, rgba(8, 217, 214, 0.95), rgba(46, 134, 222, 0.82));
}

/* 右上角柔和光晕提供层次，不会影响正文阅读对比度 */
#scenes .scene-card::after {
    content: "";
    position: absolute;
    top: -46px;
    right: -46px;
    width: 128px;
    height: 128px;
    border-radius: 50%;
    background: radial-gradient(circle at center, rgba(8, 217, 214, 0.22), rgba(8, 217, 214, 0));
    pointer-events: none;
    transition: transform 0.3s ease;
}

#scenes .scene-card h3 {
    margin-bottom: 0.75rem;
    font-size: 1.22rem;
    letter-spacing: -0.01em;
}

#scenes .scene-card p {
    color: #525f66;
    line-height: 1.75;
    font-size: 1rem;
}

#scenes .scene-card:hover {
    transform: translateY(-8px);
    border-color: rgba(8, 217, 214, 0.28);
    box-shadow: 0 20px 36px -18px rgba(37, 42, 52, 0.35);
}

#scenes .scene-card:hover::after {
    transform: scale(1.08);
}

/* 同一组卡片通过轻微色相差异区分，帮助用户快速扫读而不是逐字读完 */
#scenes .scene-card:nth-child(3n + 1)::before {
    background: linear-gradient(90deg, rgba(8, 217, 214, 0.95), rgba(46, 134, 222, 0.82));
}

#scenes .scene-card:nth-child(3n + 2)::before {
    background: linear-gradient(90deg, rgba(46, 134, 222, 0.9), rgba(255, 71, 87, 0.72));
}

#scenes .scene-card:nth-child(3n)::before {
    background: linear-gradient(90deg, rgba(255, 71, 87, 0.82), rgba(8, 217, 214, 0.88));
}

@media(max-width: 767px) {
    /* 移动端主要问题是信息密度过高，所以只收紧留白，不改结构，确保阅读节奏稳定。 */
    #scenes .scenes-grid {
        gap: 1rem;
    }

    #scenes .scene-card {
        padding: 1.5rem;
    }

    #scenes .scene-card h3 {
        font-size: 1.1rem;
    }

    #scenes .scene-card p {
        font-size: 0.95rem;
        line-height: 1.68;
    }
}

/* Timeline */
.step-num {
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background: #fff;
    color: var(--primary-teal);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 800;
    font-size: 1.2rem;
    box-shadow: var(--shadow-soft);
    flex-shrink: 0;
}

.timeline-step {
    display: flex;
    gap: 1.5rem;
    margin-bottom: 3rem;
}

/* Stats */
.stat-card {
    text-align: center;
    padding: 2rem;
    background: #fff;
    border-radius: var(--radius-card);
    box-shadow: var(--shadow-card);
}

.stat-value {
    display: block;
    font-size: 3.5rem;
    font-weight: 900;
    background: linear-gradient(135deg, var(--primary-teal), var(--accent-red));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    line-height: 1;
    margin-bottom: 0.5rem;
}

/* Accordion */
.accordion-item {
    background: #fff;
    border-radius: 20px;
    margin-bottom: 1rem;
    overflow: hidden;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.03);
}

.accordion-header {
    background: transparent;
    border: none;
    width: 100%;
    padding: 1.5rem;
    text-align: left;
    font-weight: 700;
    font-size: 1.1rem;
    color: var(--text-main);
    display: flex;
    justify-content: space-between;
    cursor: pointer;
}

.accordion-content {
    padding: 0 1.5rem;
    max-height: 0;
    overflow: hidden;
    transition: all 0.3s ease;
}

.accordion-item.active .accordion-content {
    padding-bottom: 1.5rem;
    max-height: 300px;
}

/* Footer */
.footer {
    padding: 4rem 0 2rem;
    background: rgba(255, 255, 255, 0.5);
}

.footer-link {
    color: var(--text-sub);
    text-decoration: none;
    margin: 0 1rem;
    font-weight: 600;
}

.footer-link:hover {
    color: var(--primary-teal);
}

/* Scroll Reveal */
.scroll-reveal {
    opacity: 0;
    transform: translateY(30px);
    transition: 0.8s ease;
}

.scroll-reveal.visible {
    opacity: 1;
    transform: translateY(0);
}


/* Text Decorations */
.wavy-cyan {
    text-decoration: underline wavy;
    text-decoration-color: var(--primary-teal);
    text-decoration-thickness: 2px;
    text-underline-offset: 4px;
}

.wavy-pink {
    text-decoration: underline wavy;
    text-decoration-color: var(--accent-red);
    text-decoration-thickness: 2px;
    text-underline-offset: 4px;
}

.wavy-purple {
    text-decoration: underline wavy;
    text-decoration-color: var(--primary-blue);
    text-decoration-thickness: 2px;
    text-underline-offset: 4px;
}