.lesson-page {
  --lesson-dark: #10231f;
  --lesson-yellow: #f0b94b;
  --lesson-blue: #7db6c5;
  --lesson-red: #df5b3f;
  background:
    linear-gradient(90deg, transparent 49.9%, rgb(23 33 29 / 3%) 50%, transparent 50.1%),
    var(--paper);
}

.lesson-page main,
.lesson-header,
.lesson-page footer {
  width: min(1240px, calc(100% - 48px));
}

.lesson-header {
  min-height: 88px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-inline: auto;
  border-bottom: 1px solid var(--line);
}

.lesson-progress {
  display: grid;
  grid-template-columns: auto 120px 38px;
  align-items: center;
  gap: 12px;
  color: var(--muted);
  font-family: "DM Mono", monospace;
  font-size: 9px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.progress-track {
  height: 2px;
  overflow: hidden;
  background: var(--line);
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--accent);
  transition: width 160ms ease-out;
}

.lesson-hero {
  min-height: 720px;
  display: grid;
  grid-template-columns: 1.18fr 0.82fr;
  align-items: center;
  gap: clamp(40px, 7vw, 110px);
  padding: 72px 0 100px;
}

.back-link {
  display: inline-block;
  margin-bottom: 54px;
  color: var(--muted);
  font-size: 11px;
  font-weight: 600;
  text-decoration: none;
}

.lesson-hero .eyebrow {
  margin-bottom: 24px;
}

.lesson-hero h1 {
  margin-bottom: 34px;
  font-size: clamp(66px, 8.2vw, 112px);
}

.lesson-deck {
  max-width: 650px;
  margin-bottom: 34px;
  color: var(--muted);
  font-size: 18px;
  line-height: 1.72;
}

.lesson-deck strong {
  color: var(--ink);
  font-weight: 600;
}

.start-link {
  display: inline-flex;
  gap: 16px;
  padding-bottom: 6px;
  border-bottom: 1px solid currentColor;
  font-size: 12px;
  font-weight: 600;
  text-decoration: none;
}

.hero-circuit {
  min-width: 0;
}

.circuit-loop {
  width: min(100%, 420px);
  aspect-ratio: 1;
  position: relative;
  margin-inline: auto;
  border: 2px solid var(--green);
  border-radius: 50%;
}

.circuit-loop::before,
.circuit-loop::after {
  content: "";
  position: absolute;
  inset: 18%;
  border: 1px dashed rgb(28 89 73 / 24%);
  border-radius: 50%;
}

.circuit-loop::after {
  inset: 39%;
  border: 0;
  background: rgb(168 215 189 / 30%);
}

.battery,
.resistor-mark {
  position: absolute;
  z-index: 2;
  background: var(--paper);
}

.battery {
  inset: 50% auto auto -22px;
  width: 44px;
  height: 90px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
  transform: translateY(-50%);
  color: var(--accent);
  font: 500 17px/1 "DM Mono", monospace;
}

.battery::before,
.battery::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 38px;
  height: 2px;
  background: var(--green);
  transform: translate(-50%, -8px);
}

.battery::after {
  width: 22px;
  transform: translate(-50%, 8px);
}

.resistor-mark {
  inset: 50% -23px auto auto;
  width: 46px;
  height: 88px;
  display: grid;
  place-items: center;
  transform: translateY(-50%);
  border: 1px solid var(--green);
  color: var(--green);
  font: 500 18px/1 "DM Mono", monospace;
}

.charge {
  width: 10px;
  height: 10px;
  position: absolute;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 6px rgb(223 91 63 / 12%);
}

.charge-one { top: 8%; left: 25%; }
.charge-two { right: 17%; bottom: 12%; }
.charge-three { bottom: 3%; left: 35%; }

.hero-circuit > p {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  margin: 24px 0 0;
  color: var(--muted);
  font: 400 9px/1 "DM Mono", monospace;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.hero-circuit > p span {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--mint);
  box-shadow: 0 0 0 4px rgb(168 215 189 / 20%);
}

.lesson-layout {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr);
  gap: clamp(48px, 8vw, 112px);
  padding-bottom: 120px;
  border-top: 1px solid var(--line);
}

.lesson-nav {
  height: fit-content;
  position: sticky;
  top: 28px;
  padding-top: 44px;
}

.lesson-nav > p {
  color: var(--muted);
  font: 500 9px/1 "DM Mono", monospace;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.lesson-nav ol {
  list-style: none;
  margin: 22px 0 0;
  padding: 0;
}

.lesson-nav a {
  display: grid;
  grid-template-columns: 28px 1fr;
  padding: 11px 0;
  color: var(--muted);
  font-size: 12px;
  text-decoration: none;
}

.lesson-nav a:hover,
.lesson-nav a.active {
  color: var(--accent);
}

.lesson-nav a span {
  font-family: "DM Mono", monospace;
  font-size: 8px;
}

.lesson-content {
  min-width: 0;
}

.content-section {
  padding: 112px 0;
  border-bottom: 1px solid var(--line);
  scroll-margin-top: 30px;
}

.section-kicker {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 30px;
  color: var(--accent);
  font: 500 9px/1 "DM Mono", monospace;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.section-kicker span {
  display: grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border: 1px solid currentColor;
  border-radius: 50%;
}

.section-kicker p {
  margin: 0;
}

.content-section h2 {
  max-width: 820px;
  margin-bottom: 28px;
  font-size: clamp(44px, 6vw, 76px);
  line-height: 0.98;
}

.lead {
  max-width: 690px;
  color: var(--muted);
  font-size: 19px;
  line-height: 1.7;
}

.analogy {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr;
  align-items: center;
  gap: 14px;
  margin-top: 58px;
}

.analogy > div {
  min-height: 235px;
  padding: 28px;
  border: 1px solid var(--line);
  background: var(--card);
}

.analogy > span {
  color: var(--accent);
}

.analogy-symbol {
  display: grid;
  place-items: center;
  width: 52px;
  height: 52px;
  margin-bottom: 40px;
  border-radius: 50%;
  background: var(--green);
  color: var(--card);
  font: 500 22px/1 "DM Mono", monospace;
}

.analogy strong {
  display: block;
  margin-bottom: 8px;
  font-size: 18px;
}

.analogy p,
.note p,
.direction-note p,
.safety-note p {
  margin: 0;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.6;
}

.note,
.direction-note,
.safety-note {
  display: grid;
  margin-top: 32px;
  border-left: 3px solid var(--lesson-yellow);
  background: rgb(240 185 75 / 10%);
}

.note {
  grid-template-columns: 160px 1fr;
  gap: 28px;
  padding: 22px 26px;
}

.note strong {
  font-size: 13px;
}

.quantity-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin-top: 54px;
}

.quantity-card {
  min-height: 430px;
  display: flex;
  flex-direction: column;
  padding: 26px;
  border: 1px solid var(--line);
  background: var(--card);
}

.quantity-card > div:first-child {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: 62px;
}

.quantity-card > div:first-child span {
  font: 500 64px/1 "DM Mono", monospace;
}

.quantity-card small {
  color: var(--muted);
  font: 400 9px/1 "DM Mono", monospace;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.quantity-card h3 {
  margin-bottom: 16px;
  font-size: 27px;
  font-weight: 500;
}

.quantity-card > p {
  flex: 1;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.65;
}

.quantity-card dl {
  margin: 28px 0 0;
}

.quantity-card dl div {
  display: flex;
  justify-content: space-between;
  padding: 10px 0;
  border-top: 1px solid var(--line);
  font: 400 9px/1.3 "DM Mono", monospace;
}

.quantity-card dt { color: var(--muted); }
.quantity-card dd { margin: 0; }
.voltage-card { border-top: 4px solid var(--lesson-red); }
.current-card { border-top: 4px solid var(--lesson-blue); }
.resistance-card { border-top: 4px solid var(--lesson-yellow); }

.direction-note,
.safety-note {
  grid-template-columns: auto 1fr;
  align-items: center;
  gap: 20px;
  padding: 22px 26px;
}

.direction-note > span {
  font-size: 28px;
  color: var(--green);
}

.formula-section {
  color: #f7f2e9;
  position: relative;
}

.formula-section::before {
  content: "";
  position: absolute;
  z-index: -1;
  inset: 0 calc((100vw - min(1240px, calc(100vw - 48px))) / -2);
  background: var(--lesson-dark);
}

.formula-section .section-kicker { color: var(--mint); }
.formula-section h2 { color: #f7f2e9; }

.formula-heading {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  align-items: end;
  gap: 40px;
}

.formula-heading p {
  max-width: 590px;
  margin: 28px 0 0;
  color: rgb(247 242 233 / 62%);
  line-height: 1.7;
}

.formula-lockup {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: clamp(10px, 2vw, 22px);
}

.formula-lockup span {
  display: grid;
  place-items: center;
  width: clamp(72px, 9vw, 104px);
  aspect-ratio: 1;
  border: 1px solid rgb(255 255 255 / 30%);
  border-radius: 50%;
  font: 500 clamp(30px, 4vw, 48px)/1 "DM Mono", monospace;
}

.formula-lockup span:first-child { color: #f7aa95; }
.formula-lockup span:nth-of-type(2) { color: #a9d6df; }
.formula-lockup span:last-child { color: #f0cf82; }
.formula-lockup b { font-weight: 400; }

.formula-variants {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  margin-top: 76px;
  border-block: 1px solid rgb(255 255 255 / 18%);
}

.formula-variants p {
  display: flex;
  flex-direction: column;
  gap: 18px;
  margin: 0;
  padding: 26px;
  border-right: 1px solid rgb(255 255 255 / 18%);
}

.formula-variants p:last-child { border: 0; }
.formula-variants span { color: rgb(247 242 233 / 48%); font: 400 9px/1 "DM Mono", monospace; text-transform: uppercase; }
.formula-variants strong { font: 500 20px/1 "DM Mono", monospace; }

.worked-example {
  display: grid;
  grid-template-columns: 150px 1fr;
  gap: 38px;
  margin-top: 34px;
  padding: 28px;
  background: rgb(255 255 255 / 6%);
}

.example-label {
  color: var(--mint);
  font: 400 9px/1 "DM Mono", monospace;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.worked-example h3 {
  margin-bottom: 12px;
  font-size: 20px;
  font-weight: 500;
}

.worked-example div p {
  margin: 0;
  color: rgb(247 242 233 / 62%);
}

.worked-example div p strong { color: #f7f2e9; }

.lab {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  margin-top: 52px;
  border: 1px solid var(--line);
  background: var(--card);
}

.lab-stage {
  min-height: 560px;
  display: flex;
  flex-direction: column;
  padding: 38px;
  border-right: 1px solid var(--line);
  background: #e9e4d9;
}

.lab-circuit {
  flex: 1;
  min-height: 350px;
  position: relative;
}

.lab-wire {
  position: absolute;
  inset: 42px 34px 56px;
  border: 3px solid var(--green);
  border-radius: 58px;
}

.lab-battery,
.lab-resistor,
.lab-bulb {
  position: absolute;
  z-index: 2;
  background: #e9e4d9;
}

.lab-battery {
  top: 50%;
  left: 16px;
  width: 40px;
  height: 102px;
  display: grid;
  place-items: center;
  transform: translateY(-50%);
  border: 1px solid var(--green);
  font: 500 10px/1 "DM Mono", monospace;
}

.lab-resistor {
  top: 22px;
  left: 50%;
  min-width: 100px;
  padding: 13px;
  transform: translateX(-50%);
  border: 2px solid var(--lesson-yellow);
  text-align: center;
  font: 500 10px/1 "DM Mono", monospace;
}

.lab-bulb {
  top: 50%;
  right: 8px;
  width: 60px;
  height: 84px;
  transform: translateY(-50%);
}

.bulb-glass {
  width: 58px;
  height: 58px;
  display: block;
  position: relative;
  border: 2px solid var(--green);
  border-radius: 50%;
  background: rgb(255 255 255 / 25%);
}

.bulb-glass::after {
  content: "";
  width: 23px;
  height: 21px;
  position: absolute;
  top: 56px;
  left: 15px;
  border: 2px solid var(--green);
  border-top: 0;
}

.bulb-glow {
  position: absolute;
  z-index: -1;
  inset: -18px 0 auto -18px;
  width: 94px;
  height: 94px;
  border-radius: 50%;
  background: rgb(240 185 75 / var(--glow-alpha, 0.35));
  filter: blur(12px);
}

.flow-dots i {
  width: 8px;
  height: 8px;
  position: absolute;
  z-index: 3;
  border-radius: 50%;
  background: var(--accent);
  animation: flow var(--flow-speed, 2s) linear infinite;
}

.flow-dots i:nth-child(2) { animation-delay: -0.4s; }
.flow-dots i:nth-child(3) { animation-delay: -0.8s; }
.flow-dots i:nth-child(4) { animation-delay: -1.2s; }
.flow-dots i:nth-child(5) { animation-delay: -1.6s; }

.lab-readouts {
  display: grid;
  grid-template-columns: 1fr 1fr;
  border-top: 1px solid var(--line);
}

.lab-readouts > div {
  display: flex;
  flex-direction: column;
  gap: 12px;
  padding-top: 22px;
}

.lab-readouts span {
  color: var(--muted);
  font: 400 9px/1 "DM Mono", monospace;
  text-transform: uppercase;
}

.lab-readouts output {
  font: 500 clamp(25px, 3vw, 38px)/1 "DM Mono", monospace;
}

.lab-controls {
  padding: 38px;
}

.lab-controls label {
  display: block;
  margin-bottom: 40px;
}

.lab-controls label > span:first-child,
.range-ends {
  display: flex;
  justify-content: space-between;
}

.lab-controls label strong {
  font-size: 13px;
}

.lab-controls label output {
  color: var(--accent);
  font: 500 11px/1 "DM Mono", monospace;
}

.lab-controls input[type="range"] {
  width: 100%;
  height: 3px;
  margin: 24px 0 12px;
  appearance: none;
  background: var(--line);
  accent-color: var(--accent);
}

.lab-controls input[type="range"]::-webkit-slider-thumb {
  width: 20px;
  height: 20px;
  appearance: none;
  border: 5px solid var(--card);
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 1px var(--accent);
}

.range-ends small {
  color: var(--muted);
  font: 400 8px/1 "DM Mono", monospace;
}

.lab-insight {
  display: grid;
  grid-template-columns: 26px 1fr;
  gap: 14px;
  margin-top: 8px;
  padding: 18px;
  background: rgb(168 215 189 / 20%);
}

.lab-insight span { color: var(--green); font-size: 20px; }
.lab-insight p { margin: 0; color: var(--muted); font-size: 12px; line-height: 1.55; }

.presets {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  margin-top: 22px;
}

.presets button,
.quiz button {
  border: 1px solid var(--line);
  background: transparent;
  color: var(--ink);
  cursor: pointer;
  font: 500 9px/1 "DM Mono", monospace;
  text-transform: uppercase;
}

.presets button {
  padding: 10px 12px;
  border-radius: 20px;
}

.presets button:hover,
.presets button:focus-visible {
  border-color: var(--accent);
  color: var(--accent);
}

.power-intro {
  display: grid;
  grid-template-columns: auto 1fr;
  align-items: center;
  gap: 60px;
  margin: 54px 0 70px;
}

.power-formula {
  display: flex;
  align-items: center;
  gap: 13px;
  font: 500 24px/1 "DM Mono", monospace;
}

.power-formula span {
  display: grid;
  place-items: center;
  width: 70px;
  height: 70px;
  border-radius: 50%;
  background: var(--green);
  color: var(--paper);
}

.power-intro p {
  max-width: 520px;
  margin: 0;
  color: var(--muted);
  font-size: 17px;
  line-height: 1.7;
}

.circuit-types {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

.circuit-types article {
  padding: 30px;
  border: 1px solid var(--line);
  background: var(--card);
}

.type-label {
  color: var(--accent);
  font: 500 9px/1 "DM Mono", monospace;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.mini-circuit {
  height: 120px;
  position: relative;
  margin: 22px 0 30px;
}

.mini-circuit i {
  position: absolute;
  inset: 18px;
  border: 2px solid var(--green);
}

.mini-circuit b {
  display: grid;
  place-items: center;
  position: absolute;
  z-index: 2;
  width: 54px;
  height: 28px;
  border: 1px solid var(--lesson-yellow);
  background: var(--card);
  font: 500 10px/1 "DM Mono", monospace;
}

.series-circuit b:first-of-type { top: 4px; left: 29%; }
.series-circuit b:last-of-type { top: 4px; right: 29%; }
.parallel-circuit i { inset: 18px 50px; }
.parallel-circuit i::after { content: ""; position: absolute; inset: 34px -2px auto; border-top: 2px solid var(--green); }
.parallel-circuit b:first-of-type { top: 4px; left: calc(50% - 27px); }
.parallel-circuit b:last-of-type { bottom: 4px; left: calc(50% - 27px); }

.circuit-types h3 {
  margin-bottom: 18px;
  font-size: 26px;
  font-weight: 500;
}

.circuit-types ul {
  margin: 0;
  padding-left: 18px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.9;
}

.safety-note {
  margin-top: 34px;
  border-color: var(--accent);
  background: rgb(223 91 63 / 9%);
}

.safety-note > span {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  border: 1px solid var(--accent);
  border-radius: 50%;
  color: var(--accent);
  font: 500 18px/1 "DM Mono", monospace;
}

.safety-note strong { display: block; margin-bottom: 5px; font-size: 13px; }

.quiz {
  margin-top: 54px;
}

.quiz fieldset {
  margin: 0;
  padding: 30px 0;
  border: 0;
  border-top: 1px solid var(--line);
}

.quiz legend {
  width: 100%;
  margin-bottom: 22px;
  font-size: 18px;
  font-weight: 600;
}

.quiz legend span {
  margin-right: 18px;
  color: var(--accent);
  font: 500 9px/1 "DM Mono", monospace;
}

.quiz fieldset > label {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin: 0 8px 8px 0;
  padding: 12px 16px;
  border: 1px solid var(--line);
  border-radius: 24px;
  background: var(--card);
  cursor: pointer;
  font-size: 12px;
}

.quiz input { accent-color: var(--accent); }
.quiz fieldset.correct { border-top-color: var(--green); }
.quiz fieldset.incorrect { border-top-color: var(--accent); }

.answer-note {
  min-height: 20px;
  margin: 10px 0 0;
  color: var(--muted);
  font-size: 12px;
}

.quiz-actions {
  display: flex;
  align-items: center;
  gap: 22px;
  padding-top: 28px;
  border-top: 1px solid var(--line);
}

.quiz button {
  padding: 15px 20px;
  border-color: var(--ink);
  background: var(--ink);
  color: var(--paper);
}

.quiz button:hover { background: var(--accent); border-color: var(--accent); }
.quiz-actions output { color: var(--muted); font-size: 12px; }

.lesson-summary {
  padding: 110px 0 40px;
  text-align: center;
}

.lesson-summary h2 {
  max-width: 750px;
  margin: 0 auto 52px;
}

.lesson-summary > div {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  margin-bottom: 40px;
  border-block: 1px solid var(--line);
}

.lesson-summary > div p {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin: 0;
  padding: 24px 12px;
  border-right: 1px solid var(--line);
}

.lesson-summary > div p:last-child { border: 0; }
.lesson-summary > div span { color: var(--muted); font-size: 11px; }
.lesson-summary a { font-size: 12px; font-weight: 600; text-decoration: none; }

@keyframes flow {
  0% { top: 38px; left: 17%; }
  25% { top: 38px; left: 80%; }
  50% { top: 82%; left: 80%; }
  75% { top: 82%; left: 17%; }
  100% { top: 38px; left: 17%; }
}

@media (max-width: 960px) {
  .lesson-hero { grid-template-columns: 1fr; }
  .hero-circuit { width: min(440px, 78vw); margin-inline: auto; }
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-nav { display: none; }
  .formula-heading,
  .lab { grid-template-columns: 1fr; }
  .formula-lockup { justify-content: flex-start; margin-top: 30px; }
  .lab-stage { border-right: 0; border-bottom: 1px solid var(--line); }
}

@media (max-width: 720px) {
  .lesson-page main,
  .lesson-header,
  .lesson-page footer { width: min(100% - 32px, 1240px); }
  .lesson-progress { grid-template-columns: 84px 30px; }
  .lesson-progress > span:first-child { display: none; }
  .lesson-hero { padding: 54px 0 78px; }
  .back-link { margin-bottom: 40px; }
  .lesson-hero h1 { font-size: clamp(55px, 16vw, 82px); }
  .content-section { padding: 78px 0; }
  .content-section h2 { font-size: clamp(40px, 12vw, 60px); }
  .analogy,
  .quantity-grid,
  .formula-variants,
  .circuit-types { grid-template-columns: 1fr; }
  .analogy > span { transform: rotate(90deg); justify-self: center; }
  .quantity-card { min-height: 350px; }
  .note,
  .worked-example { grid-template-columns: 1fr; gap: 12px; }
  .formula-variants p { border-right: 0; border-bottom: 1px solid rgb(255 255 255 / 18%); }
  .lab-stage,
  .lab-controls { padding: 24px; }
  .lab-stage { min-height: 490px; }
  .lab-wire { inset-inline: 20px; }
  .power-intro { grid-template-columns: 1fr; gap: 28px; }
  .lesson-summary > div { grid-template-columns: 1fr 1fr; }
  .lesson-summary > div p:nth-child(2) { border-right: 0; }
  .lesson-summary > div p:nth-child(-n + 2) { border-bottom: 1px solid var(--line); }
  .quiz-actions { align-items: flex-start; flex-direction: column; }
}

@media (prefers-reduced-motion: reduce) {
  .flow-dots i { animation: none; }
}