:root {
  --void: #05070b;
  --panel: #0c1118;
  --panel-2: #101923;
  --ink: #eef7ff;
  --muted: #9db0c4;
  --line: rgba(90, 227, 255, 0.22);
  --cyan: #27e7ff;
  --lime: #b7ff3c;
  --magenta: #ff2bd6;
  --amber: #ffd64d;
  --danger: #ff4b6a;
  --shadow: 0 18px 42px rgba(0, 0, 0, 0.34);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at 12% 0%, rgba(39, 231, 255, 0.09), transparent 30%),
    radial-gradient(circle at 88% 12%, rgba(255, 43, 214, 0.08), transparent 28%),
    var(--void);
  font-family: Inter, Segoe UI, Roboto, Arial, sans-serif;
  line-height: 1.55;
}

header {
  min-height: 300px;
  display: grid;
  align-items: end;
  padding: 34px 18px;
  background:
    linear-gradient(90deg, rgba(5, 7, 11, 0.98), rgba(12, 17, 24, 0.88)),
    repeating-linear-gradient(115deg, rgba(39, 231, 255, 0.08) 0 2px, transparent 2px 28px);
  border-bottom: 1px solid var(--line);
}

.wrap {
  width: min(1180px, 100%);
  margin: 0 auto;
}

.eyebrow {
  color: var(--lime);
  font-weight: 900;
  letter-spacing: .08em;
  text-transform: uppercase;
  font-size: .82rem;
}

h1 {
  margin: 8px 0 12px;
  max-width: 920px;
  font-size: clamp(2.15rem, 5vw, 4.8rem);
  line-height: .98;
  letter-spacing: 0;
}

.lead {
  max-width: 860px;
  color: var(--muted);
  font-size: 1.08rem;
}

nav {
  position: sticky;
  top: 0;
  z-index: 5;
  background: rgba(5, 7, 11, 0.94);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(10px);
}

nav .wrap {
  display: flex;
  gap: 8px;
  overflow-x: auto;
  padding: 10px 16px;
}

nav a {
  color: var(--cyan);
  text-decoration: none;
  font-weight: 800;
  white-space: nowrap;
  padding: 8px 10px;
  border-radius: 6px;
}

nav a:hover { background: rgba(39, 231, 255, 0.12); }

main {
  width: min(1180px, 100%);
  margin: 0 auto;
  padding: 26px 16px 54px;
}

section {
  padding: 26px 0;
  border-bottom: 1px solid var(--line);
}

h2 {
  margin: 0 0 12px;
  font-size: clamp(1.55rem, 3vw, 2.25rem);
  letter-spacing: 0;
}

h3 {
  margin: 0 0 8px;
  font-size: 1.08rem;
}

.intro {
  max-width: 900px;
  color: var(--muted);
}

.grid {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 16px;
  align-items: start;
}

.card {
  background: linear-gradient(180deg, var(--panel-2), var(--panel));
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
  padding: 18px;
}

.span-4 { grid-column: span 4; }
.span-5 { grid-column: span 5; }
.span-6 { grid-column: span 6; }
.span-7 { grid-column: span 7; }
.span-8 { grid-column: span 8; }
.span-12 { grid-column: span 12; }

.formula {
  margin: 12px 0;
  padding: 12px 14px;
  color: var(--ink);
  background: rgba(39, 231, 255, 0.07);
  border: 1px solid var(--line);
  border-left: 4px solid var(--cyan);
  border-radius: 6px;
  font-family: Cambria Math, STIX Two Math, Georgia, serif;
  font-size: 1.05rem;
  overflow-x: auto;
}

.formula div { margin: 4px 0; }
.formula sup, .formula sub { line-height: 0; }

.eq {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  min-height: 34px;
}

.frac {
  display: inline-grid;
  grid-template-rows: auto auto;
  align-items: center;
  text-align: center;
  vertical-align: middle;
  line-height: 1.15;
  margin: 0 3px;
}

.frac .top {
  padding: 0 6px 3px;
  border-bottom: 1px solid currentColor;
}

.frac .bottom {
  padding: 3px 6px 0;
}

.sqrt {
  border-top: 1px solid currentColor;
  padding: 1px 4px 0 7px;
  position: relative;
}

.sqrt::before {
  content: "√";
  position: absolute;
  left: -8px;
  top: -2px;
}

.example {
  padding: 12px;
  border-radius: 6px;
  color: #ffe8a0;
  background: rgba(255, 214, 77, 0.08);
  border: 1px solid rgba(255, 214, 77, 0.32);
}

.lesson {
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(280px, .9fr);
  gap: 18px;
  align-items: start;
}

.lesson-text {
  font-size: 1rem;
}

.lesson-text p {
  color: var(--muted);
  margin: 0 0 12px;
}

.callout {
  padding: 14px;
  border-radius: 8px;
  background: rgba(39, 231, 255, 0.07);
  border: 1px solid var(--line);
}

.callout strong {
  color: var(--cyan);
}

.worked {
  margin-top: 14px;
  padding: 14px;
  border-radius: 8px;
  background: rgba(183, 255, 60, 0.07);
  border: 1px solid rgba(183, 255, 60, 0.25);
}

.worked h3,
.case-study h3,
.interpretation h3 {
  color: var(--lime);
}

.calc-line {
  display: grid;
  grid-template-columns: 190px 1fr;
  gap: 10px;
  padding: 7px 0;
  border-bottom: 1px solid rgba(90, 227, 255, 0.14);
}

.calc-line span:first-child {
  color: var(--ink);
  font-weight: 800;
}

.calc-line span:last-child {
  font-family: Cambria Math, STIX Two Math, Georgia, serif;
  color: var(--ink);
}

.case-study {
  padding: 16px;
  border-radius: 8px;
  background: linear-gradient(180deg, rgba(255, 43, 214, 0.08), rgba(12, 17, 24, 0.9));
  border: 1px solid rgba(255, 43, 214, 0.25);
}

.interpretation {
  padding: 16px;
  border-radius: 8px;
  background: rgba(255, 214, 77, 0.07);
  border: 1px solid rgba(255, 214, 77, 0.26);
}

.learning-list {
  margin: 0;
  padding-left: 18px;
  color: var(--muted);
}

.learning-list li { margin: 7px 0; }

.technical {
  color: var(--muted);
}

.steps {
  padding-left: 18px;
  margin: 10px 0 0;
}

.steps li { margin: 6px 0; }

.diagram {
  width: 100%;
  height: 310px;
  display: block;
  background: #090d0f;
  border: 1px solid var(--line);
  border-radius: 8px;
}

.rcs-polar-diagram {
  height: 430px;
}

.module-link {
  display: block;
  min-height: 170px;
  color: inherit;
  text-decoration: none;
}

.module-link h3 { color: var(--cyan); }
.module-link:hover { border-color: rgba(183, 255, 60, 0.55); }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: .92rem;
}

th, td {
  padding: 8px;
  border-bottom: 1px solid var(--line);
  text-align: left;
}

th {
  color: var(--cyan);
  background: rgba(39, 231, 255, 0.08);
}

footer {
  width: min(1180px, 100%);
  margin: 0 auto;
  padding: 30px 16px 44px;
  color: var(--muted);
}

@media (max-width: 860px) {
  header { min-height: 270px; }
  .span-4, .span-5, .span-6, .span-7, .span-8 { grid-column: span 12; }
  .diagram { height: 250px; }
  .rcs-polar-diagram { height: 330px; }
  .lesson { grid-template-columns: 1fr; }
  .calc-line { grid-template-columns: 1fr; }
}