:root {
  --bg: #f4f8fd;
  --surface: rgba(255, 255, 255, 0.84);
  --text: #0f172a;
  --muted: #0f172a;
  --line: rgba(37, 99, 235, 0.14);
  --primary: #2563eb;
  --primary-2: #06b6d4;
  --shadow: 0 16px 44px rgba(37, 99, 235, 0.1);
  --radius: 24px;
  --max: 1140px;
  --mono:
    ui-monospace, SFMono-Regular, "JetBrains Mono", Menlo, Consolas, monospace;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  font-family: "Inter", sans-serif;
  background: linear-gradient(180deg, #f9fbff 0%, var(--bg) 100%);
  color: var(--text);
}

.back {
  position: fixed;
  left: 18px;
  top: 18px;
  z-index: 50;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: rgba(255, 255, 255, 0.76);
  backdrop-filter: blur(10px);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 10px 16px;
  text-decoration: none;
  color: var(--primary);
  font-weight: 700;
  font-size: 14px;
  box-shadow: var(--shadow);
  transition:
    transform 0.18s ease,
    box-shadow 0.18s ease;
}
.back:hover {
  transform: translateY(-2px);
  box-shadow: 0 18px 36px rgba(37, 99, 235, 0.16);
}

.wrap {
  max-width: var(--max);
  margin: 0 auto;
  padding: 70px 24px 40px;
}

.paper {
  position: relative;
  overflow: hidden;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 32px;
  backdrop-filter: blur(18px);
  box-shadow: var(--shadow);
}
.paper:before {
  content: "";
  position: absolute;
  top: -90px;
  right: -70px;
  width: 260px;
  height: 260px;
  border-radius: 50%;
  background: rgba(37, 99, 235, 0.14);
  filter: blur(46px);
  z-index: 0;
}
.paper:after {
  content: "";
  position: absolute;
  bottom: -70px;
  left: -40px;
  width: 200px;
  height: 200px;
  border-radius: 50%;
  background: rgba(6, 182, 212, 0.12);
  filter: blur(46px);
  z-index: 0;
}

.head {
  position: relative;
  z-index: 1;
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  padding: 26px 30px 6px;
}
.sub {
  display: inline-flex;
  padding: 6px 12px;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.7);
  font-size: 12.5px;
  font-weight: 700;
  color: var(--primary);
}

.content {
  position: relative;
  z-index: 1;
  padding: 6px 30px 28px;
}
.title {
  font-family: "Plus Jakarta Sans", sans-serif;
  font-size: clamp(1.9rem, 4vw, 2.6rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  margin: 6px 0 4px;
  background: linear-gradient(90deg, var(--primary), var(--primary-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.row {
  display: grid;
  grid-template-columns: 220px 1.05fr 0.95fr;
  gap: 20px;
  padding: 20px 0;
  border-top: 1px dashed var(--line);
  align-items: start;
}
.row.wider {
  grid-template-columns: 230px 1.05fr 0.95fr;
}

.label {
  font-family: "Plus Jakarta Sans", sans-serif;
  font-size: 15px;
  line-height: 1.3;
  font-weight: 800;
  color: var(--text);
}
.body {
  font-size: 15.5px;
  line-height: 1.55;
  color: var(--muted);
}
.example {
  font-family: var(--mono);
  font-size: 14.5px;
  line-height: 1.7;
  white-space: pre-line;
  background: rgba(37, 99, 235, 0.05);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 14px 16px;
  color: var(--text);
}

.formula {
  font-family: "Plus Jakarta Sans", sans-serif;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--primary);
}

.chip {
  display: inline-block;
  padding: 5px 11px;
  border-radius: 999px;
  background: rgba(37, 99, 235, 0.08);
  color: var(--primary);
  font-weight: 700;
  font-size: 12px;
  margin-bottom: 0.5rem;
}

.footer {
  position: relative;
  z-index: 1;
  padding: 0 30px 26px;
  color: var(--muted);
  font-size: 13px;
}

.sketchbox {
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 12px;
  background: rgba(255, 255, 255, 0.6);
}
svg {
  width: 100%;
  height: auto;
  display: block;
}

.mathline {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
}
.tiny {
  font-size: 13px;
  color: var(--muted);
}
.break {
  height: 8px;
}

@media (max-width: 980px) {
  .row,
  .row.wider {
    grid-template-columns: 1fr;
  }
  .wrap {
    padding: 60px 14px 30px;
  }
  .head {
    padding: 18px 18px 6px;
  }
  .content {
    padding: 6px 18px 22px;
  }
  .footer {
    padding: 0 18px 22px;
  }
}