/* 错题刷 · 品牌落地页
   纸感米白 / 朱砂红 / 墨黑 —— 与 App 视觉系统同源 */

:root {
  --paper: #FAF7F2;
  --paper-deep: #F1EAE0;
  --vermilion: #E4572E;
  --vermilion-deep: #C4441F;
  --ink: #26221E;
  --ash: #8C857C;
  --hairline: #E8E2D9;

  /* 不用 Google Fonts（国内常被墙/超时）；走系统宋体栈 */
  --font-display: "Songti SC", "STSong", "SimSun", "Noto Serif CJK SC", serif;
  --font-body: -apple-system, "PingFang SC", "Microsoft Yahei", "Helvetica Neue", sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  -webkit-font-smoothing: antialiased;
}

a {
  text-decoration: none;
}

/* ---------- Hero ---------- */

.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 8vh 6vw;
  overflow: hidden;
  background: var(--paper);
}

.hero__atmosphere {
  position: absolute;
  inset: 0;
  z-index: 0;
  background:
    radial-gradient(60% 55% at 82% 8%, rgba(228, 87, 46, 0.16), transparent 70%),
    radial-gradient(50% 45% at 6% 96%, rgba(228, 87, 46, 0.10), transparent 70%),
    linear-gradient(160deg, var(--paper) 0%, var(--paper) 55%, var(--paper-deep) 100%);
}

.hero__atmosphere::after {
  content: "";
  position: absolute;
  inset: 0;
  opacity: 0.5;
  mix-blend-mode: multiply;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='160' height='160'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/%3E%3CfeColorMatrix type='matrix' values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.04 0'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

.seal {
  position: absolute;
  top: 6vh;
  right: 6vw;
  z-index: 2;
  width: 3.4rem;
  height: 3.4rem;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--vermilion);
  color: var(--paper);
  font-family: var(--font-display);
  font-weight: 900;
  font-size: 1.7rem;
  border-radius: 6px;
  transform: rotate(4deg);
  box-shadow: 0 6px 18px rgba(228, 87, 46, 0.35);
}

.hero__content {
  position: relative;
  z-index: 1;
  max-width: 46rem;
  text-align: center;
}

.hero__domain {
  margin: 0 0 1.4rem;
  font-size: 0.85rem;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--ash);
  font-weight: 600;
}

.brand {
  position: relative;
  margin: 0;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(4.2rem, 15vw, 9rem);
  line-height: 1;
  letter-spacing: 0.03em;
  color: var(--ink);
}

.brand__stroke {
  display: block;
  width: clamp(6rem, 22vw, 11rem);
  height: 0.5rem;
  margin: 1.1rem auto 0;
  background: var(--vermilion);
  border-radius: 999px;
  transform: rotate(-1.2deg) scaleX(1.02);
  opacity: 0.9;
}

.slogan {
  margin: 2rem 0 0;
  font-family: var(--font-display);
  font-weight: 700;
  font-size: clamp(1.5rem, 3.4vw, 2.2rem);
  color: var(--vermilion-deep);
  letter-spacing: 0.02em;
}

.support {
  margin: 1.1rem 0 0;
  font-size: clamp(1rem, 1.6vw, 1.15rem);
  color: var(--ash);
  font-weight: 500;
}

.cta {
  margin-top: 2.8rem;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 1rem 1.2rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  padding: 0.95rem 1.7rem;
  border-radius: 999px;
  font-size: 1rem;
  font-weight: 700;
  white-space: nowrap;
}

.btn--primary {
  background: var(--ink);
  color: var(--paper);
  transition: background 0.15s ease, transform 0.15s ease;
}

.btn--primary:hover {
  background: var(--vermilion);
  transform: translateY(-1px);
}

.btn__icon {
  width: 1.15rem;
  height: 1.15rem;
  fill: currentColor;
}

.link--more {
  color: var(--ash);
  font-size: 0.95rem;
  font-weight: 600;
  padding: 0.6rem 0.4rem;
  border-bottom: 1px solid transparent;
  transition: color 0.15s ease, border-color 0.15s ease;
}

.link--more:hover {
  color: var(--vermilion-deep);
  border-color: currentColor;
}

/* ---------- Product / three steps ---------- */

.product {
  padding: 7rem 6vw 6rem;
  background: var(--paper);
  border-top: 1px solid var(--hairline);
}

.steps {
  max-width: 68rem;
  margin: 0 auto;
  padding: 0;
  list-style: none;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 3rem;
}

.step {
  text-align: left;
}

.step__no {
  display: block;
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1rem;
  color: var(--vermilion);
  letter-spacing: 0.08em;
  margin-bottom: 0.9rem;
}

.step__title {
  margin: 0 0 0.6rem;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: 1.9rem;
  color: var(--ink);
}

.step__desc {
  margin: 0;
  font-size: 1rem;
  line-height: 1.6;
  color: var(--ash);
  max-width: 22rem;
}

@media (max-width: 780px) {
  .steps {
    grid-template-columns: 1fr;
    gap: 2.6rem;
  }

  .step {
    text-align: center;
  }

  .step__desc {
    margin-inline: auto;
  }

  .seal {
    top: 5vh;
    right: 5vw;
    width: 2.8rem;
    height: 2.8rem;
    font-size: 1.4rem;
  }
}

/* ---------- Footer ---------- */

.footer {
  padding: 2.4rem 6vw 3rem;
  text-align: center;
  border-top: 1px solid var(--hairline);
  background: var(--paper);
}

.footer p {
  margin: 0;
  font-size: 0.85rem;
  color: var(--ash);
  letter-spacing: 0.03em;
}