:root {
  --paper:#f6f5ee;
  --ink:#22323e;
  --muted:#637078;
  --line:#d9ded8;
  --blue:#315ed8;
  --lime:#e5ed64;
  --white:#fffefa;
  --radius:18px;
  font-family:"Segoe UI","Apple SD Gothic Neo","Malgun Gothic",sans-serif;
  color:var(--ink);
  background:var(--paper);
  font-synthesis:none;
  scroll-behavior:smooth;
}
* {
  box-sizing:border-box;
}
body {
  margin:0;
}
button,input,textarea {
  font:inherit;
}
button,a {
  -webkit-tap-highlight-color:transparent;
}
a {
  color:inherit;
  text-underline-offset:4px;
}
button {
  cursor:pointer;
  color:inherit;
}
button:disabled {
  cursor:default;
}
button,a,summary,textarea {
  outline-offset:5px;
}
button:focus-visible,a:focus-visible,summary:focus-visible,textarea:focus-visible {
  outline:3px solid var(--blue);
}
img {
  display:block;
  max-width:100%;
  height:auto;
}
figure,p,h1,h2,h3 {
  margin:0;
}
button {
  border:0;
}
section {
  scroll-margin-top:105px;
}
p {
  line-height:1.8;
  word-break:keep-all;
}
h1,h2,h3 {
  word-break:keep-all;
}
::selection {
  background:var(--lime);
}
.page-width {
  width:min(1340px,calc(100% - 100px));
  margin-inline:auto;
}
.skip-link {
  position:fixed;
  top:-80px;
  left:10px;
  z-index:100;
  background:var(--ink);
  color:white;
  padding:14px;
}
.skip-link:focus {
  top:10px;
}
.site-header {
  height:92px;
  padding:0 50px;
  display:flex;
  justify-content:space-between;
  align-items:center;
  border-bottom:1px solid var(--line);
  background:#f6f5eef5;
  position:sticky;
  top:0;
  z-index:30;
  backdrop-filter:blur(12px);
}
.brand {
  display:flex;
  align-items:center;
  gap:12px;
  text-decoration:none;
  font-size:18px;
  font-weight:750;
  letter-spacing:-.5px;
}
.brand small {
  display:block;
  font-size:9px;
  font-weight:600;
  letter-spacing:1.6px;
  margin-top:5px;
}
.element-mark {
  display:flex;
  position:relative;
  align-items:center;
  justify-content:center;
  width:43px;
  height:47px;
  background:var(--lime);
  border:1px solid var(--ink);
  border-radius:7px;
  font-size:26px;
  letter-spacing:-1px;
  line-height:1;
}
.element-mark small {
  position:absolute;
  font-size:8px;
  top:0;
  left:5px;
  letter-spacing:0;
}
.header-right {
  display:flex;
  align-items:center;
  gap:30px;
  font-size:13px;
}
.edition {
  border:1px solid #cbd0c7;
  padding:8px 13px;
  border-radius:30px;
}
.text-link {
  text-decoration:none;
  font-weight:600;
}
.text-link span {
  margin-left:10px;
}
.hero {
  min-height:640px;
  padding-block:70px 80px;
  display:grid;
  grid-template-columns:1.12fr 1fr;
  gap:48px;
  align-items:center;
}
.eyebrow {
  font-size:12px;
  letter-spacing:.8px;
  font-weight:650;
}
.live-dot {
  display:inline-block;
  width:7px;
  height:7px;
  border-radius:50%;
  background:var(--blue);
  margin-right:8px;
}
.hero h1 {
  font-size:clamp(40px,4.4vw,66px);
  letter-spacing:-3.6px;
  font-weight:760;
  line-height:1.25;
  margin:25px 0;
}
.hero h1>span {
  position:relative;
  z-index:0;
  white-space:nowrap;
}
.hero h1>span:after {
  content:"";
  position:absolute;
  bottom:4px;
  left:-3px;
  right:-6px;
  height:22px;
  background:var(--lime);
  z-index:-1;
  transform:rotate(-2deg);
}
.hero-intro {
  font-size:17px;
  color:var(--muted);
  margin-bottom:29px;
  letter-spacing:-.4px;
}
.button {
  display:inline-flex;
  gap:28px;
  align-items:center;
  justify-content:center;
  text-decoration:none;
  padding:16px 22px;
  border-radius:8px;
  font-size:14px;
  font-weight:650;
  transition:transform .2s,background .2s;
  min-height:48px;
}
.button:hover {
  transform:translateY(-2px);
}
.primary {
  background:var(--ink);
  color:white;
}
.primary:hover {
  background:#365060;
}
.secondary {
  background:var(--ink);
  color:white;
  font-size:12px;
  padding:12px 16px;
  gap:15px;
}
.hero-footnote {
  font-size:11px;
  margin-top:27px;
  color:var(--muted);
}
.hero-footnote span {
  margin-left:12px;
}
.hero-figure {
  padding:4px 10px;
}
.photo-paper {
  position:relative;
  background:var(--white);
  border:1px solid #e1e2d8;
  border-radius:5px;
  padding:15px 24px 20px;
  box-shadow:8px 14px 0 #e8e9e0;
  transform:rotate(2deg);
}
.photo-paper img {
  width:100%;
  height:330px;
  object-fit:contain;
  mix-blend-mode:multiply;
}
.photo-index {
  font-family:monospace;
  font-size:10px;
  letter-spacing:2px;
  color:var(--muted);
}
.photo-label {
  font-size:12px;
  line-height:1.8;
  display:block;
}
.photo-label strong {
  font-size:15px;
}
.photo-sticker {
  position:absolute;
  right:24px;
  bottom:23px;
  border:1px solid var(--ink);
  border-radius:50%;
  width:79px;
  height:79px;
  display:flex;
  flex-direction:column;
  align-items:center;
  justify-content:center;
  line-height:1.2;
  font-family:Georgia,serif;
  font-size:15px;
  background:var(--lime);
  transform:rotate(-12deg);
}
.hero-figure>figcaption {
  font-size:10px;
  line-height:1.9;
  color:var(--muted);
  margin:24px 0 0 10px;
}
.learning-layout {
  display:grid;
  grid-template-columns:210px minmax(0,1fr);
  gap:58px;
  border-top:1px solid var(--line);
}
.study-nav {
  position:sticky;
  top:130px;
  align-self:start;
  padding-top:35px;
}
.study-nav .eyebrow {
  font-size:10px;
  letter-spacing:1px;
  color:var(--muted);
  margin-bottom:23px;
}
.study-nav nav {
  display:flex;
  flex-direction:column;
  gap:5px;
}
.study-nav nav a {
  display:flex;
  gap:16px;
  align-items:center;
  padding:12px 13px;
  text-decoration:none;
  font-size:13px;
  border-radius:7px;
  transition:background .2s;
}
.study-nav nav a span {
  font-family:monospace;
  color:var(--muted);
  font-size:11px;
}
.study-nav nav a.active {
  background:#e9ecdE;
  font-weight:700;
}
.study-nav nav a.active span {
  color:var(--blue);
}
.nav-progress {
  margin:36px 12px 0;
  font-size:11px;
}
.progress-track {
  height:4px;
  background:#e0e3d9;
  margin:13px 0;
}
.progress-track span {
  display:block;
  width:0;
  height:100%;
  background:var(--blue);
  transition:width .3s;
}
.nav-progress small {
  font-size:10px;
  color:var(--muted);
}
.nav-note {
  border-top:1px solid var(--line);
  margin:30px 12px;
  padding-top:20px;
  color:var(--muted);
}
.nav-note>span {
  font-size:24px;
  color:var(--blue);
}
.nav-note p {
  font-size:11px;
  margin-top:8px;
}
.lesson {
  padding:64px 0;
  border-bottom:1px solid var(--line);
}
.section-number {
  font-family:monospace;
  font-size:11px;
  color:var(--blue);
  letter-spacing:1.6px;
  margin-bottom:18px;
}
.lesson h2 {
  font-size:36px;
  letter-spacing:-1.7px;
  line-height:1.35;
  font-weight:740;
}
.section-intro {
  color:var(--muted);
  font-size:14px;
  margin:20px 0 30px;
  max-width:700px;
}
.section-intro strong {
  color:var(--ink);
  font-weight:600;
}
.photo-grid {
  display:grid;
  grid-template-columns:repeat(3,minmax(0,1fr));
  gap:15px;
}
.image-button {
  display:block;
  width:100%;
  background:white;
  position:relative;
  border:1px solid var(--line);
  border-radius:10px;
  overflow:hidden;
  padding:10px;
  aspect-ratio:1.12;
}
.image-button img {
  width:100%;
  height:100%;
  object-fit:contain;
  transition:transform .4s;
}
.image-button:hover img {
  transform:scale(1.055);
}
.zoom-icon {
  position:absolute;
  right:8px;
  bottom:8px;
  background:var(--paper);
  border-radius:50%;
  height:27px;
  width:27px;
  display:grid;
  place-items:center;
}
.photo-grid figcaption {
  padding:15px 2px;
}
.image-step {
  font-family:monospace;
  font-size:10px;
  letter-spacing:1px;
  color:var(--blue);
}
.photo-grid h3 {
  font-size:16px;
  margin:9px 0;
}
.photo-grid p {
  font-size:12px;
  color:var(--muted);
  line-height:1.8;
}
.photo-grid figcaption a {
  display:inline-block;
  font-size:10px;
  color:var(--muted);
  margin-top:12px;
}
.image-note {
  font-size:11px;
  color:var(--muted);
  margin:12px 0 20px;
  line-height:1.7;
}
.takeaway {
  display:flex;
  gap:18px;
  background:#eaf0e9;
  border-radius:10px;
  padding:21px 25px;
  margin-top:26px;
}
.takeaway>span {
  font-size:23px;
  color:var(--blue);
}
.takeaway p {
  font-size:13px;
}
.takeaway strong {
  font-weight:650;
}
.source-line {
  font-size:10px;
  color:var(--muted);
  margin:22px 0;
  display:flex;
  flex-wrap:wrap;
  gap:6px 13px;
}
.use-grid {
  display:grid;
  grid-template-columns:repeat(3,1fr);
  gap:18px;
  margin-bottom:26px;
}
.use-grid article {
  padding:23px 19px;
  background:var(--white);
  border:1px solid var(--line);
  border-radius:11px;
}
.use-symbol {
  width:38px;
  height:38px;
  background:#eef0e6;
  color:var(--blue);
  display:grid;
  place-items:center;
  border-radius:50%;
  font-size:28px;
  margin-bottom:20px;
}
.use-grid h3 {
  font-size:15px;
  margin-bottom:10px;
}
.use-grid p {
  font-size:12px;
  color:var(--muted);
}
.plain-explanation {
  font-size:14px;
  margin-bottom:24px;
}
details {
  border-bottom:1px solid var(--line);
  background:transparent;
}
summary {
  padding:19px 32px 19px 0;
  font-size:14px;
  font-weight:600;
  cursor:pointer;
  position:relative;
  list-style:none;
  line-height:1.7;
}
summary::-webkit-details-marker {
  display:none;
}
summary:after {
  content:"＋";
  position:absolute;
  right:3px;
  top:18px;
  color:var(--blue);
}
details[open]>summary:after {
  content:"−";
}
.details-body {
  padding:0 24px 22px 0;
  color:var(--muted);
  font-size:13px;
}
.details-body p+p {
  margin-top:12px;
}
.complete-button {
  background:transparent;
  border:1px solid #bfc9bd;
  border-radius:30px;
  padding:10px 16px;
  font-size:12px;
  min-height:44px;
}
.complete-button span {
  margin-right:7px;
  color:var(--blue);
}
.complete-button[aria-pressed=true] {
  background:var(--lime);
  border-color:var(--lime);
}
.experiment {
  background:#edf1f4;
  border:1px solid #d2dbe1;
  border-radius:var(--radius);
  padding:24px;
  overflow:hidden;
}
.experiment-top {
  display:flex;
  justify-content:space-between;
  align-items:center;
}
.experiment-label {
  font-size:12px;
  display:flex;
  gap:8px;
  align-items:center;
}
.status-led {
  height:7px;
  width:7px;
  background:#a8b0b7;
  border-radius:50%;
}
.is-powered .status-led {
  background:#3b8849;
  box-shadow:0 0 0 4px #3b88491a;
}
.power-button {
  background:var(--ink);
  color:white;
  min-height:44px;
  padding:10px 17px;
  border-radius:30px;
  font-size:12px;
  display:flex;
  gap:10px;
  align-items:center;
}
.power-button span {
  font-size:21px;
  line-height:1;
}
.power-button[aria-pressed=true] {
  background:var(--lime);
  color:var(--ink);
}
.cell-diagram {
  height:290px;
  position:relative;
  max-width:600px;
  margin:25px auto 5px;
}
.chamber {
  position:absolute;
  top:65px;
  height:140px;
  border:2px solid #c6d5e0;
  border-radius:10px;
  overflow:hidden;
}
.oxygen-chamber {
  left:17%;
  width:27%;
  background:linear-gradient(to top,#dbeaf1 65%,#f5f8fa 65%);
}
.hydrogen-chamber {
  left:58%;
  width:27%;
  background:linear-gradient(to top,#e0e8f7 65%,#f5f8fa 65%);
}
.chamber-label {
  position:absolute;
  left:0;
  right:0;
  bottom:10px;
  text-align:center;
  font-size:10px;
  line-height:1.8;
  z-index:3;
}
.chamber-label strong {
  font-weight:600;
  font-size:11px;
}
.titanium-layer {
  position:absolute;
  top:65px;
  left:44%;
  width:5%;
  height:140px;
  background-color:#e7e99d;
  background-image:radial-gradient(#839249 1px,transparent 1px);
  background-size:6px 6px;
  border:1px solid #9ba75f;
  z-index:2;
  border-radius:3px;
}
.titanium-layer span {
  position:absolute;
  bottom:8px;
  left:0;
  right:0;
  text-align:center;
  font-family:Georgia,serif;
  font-size:14px;
}
.reaction-layer {
  position:absolute;
  top:65px;
  height:140px;
  width:1.5%;
  background:#566c7a;
}
.left-reaction {
  left:49%;
}
.right-reaction {
  left:56.5%;
}
.membrane {
  position:absolute;
  left:50.5%;
  width:6%;
  top:55px;
  height:160px;
  background:#fafaf6;
  border:1px solid #b8c4ce;
  z-index:1;
  display:flex;
  align-items:flex-end;
  justify-content:center;
  padding-bottom:10px;
  font-size:11px;
}
.proton {
  position:absolute;
  top:55px;
  left:0;
  font-size:11px;
  font-weight:700;
  color:var(--blue);
  white-space:nowrap;
  opacity:0;
}
.gas-label {
  position:absolute;
  top:4px;
  font-size:11px;
  display:flex;
  gap:8px;
  align-items:center;
}
.gas-label>span {
  font-size:23px;
  font-family:Georgia,serif;
}
.oxygen-label {
  left:22%;
}
.hydrogen-label {
  left:64%;
}
.flow-arrow {
  font-size:22px;
  opacity:.2;
}
.water-feed {
  position:absolute;
  left:1%;
  top:120px;
  font-size:11px;
  color:var(--blue);
}
.water-feed span {
  font-size:19px;
  margin-left:5px;
}
.power-wire {
  position:absolute;
  top:205px;
  left:29%;
  width:43%;
  height:45px;
  border:2px solid #95a3b0;
  border-top:0;
  border-radius:0 0 15px 15px;
}
.power-wire span {
  position:absolute;
  top:32px;
  width:240px;
  left:50%;
  transform:translateX(-50%);
  text-align:center;
  background:#edf1f4;
  padding:4px;
  font-size:10px;
  color:var(--muted);
}
.bubble {
  position:absolute;
  width:9px;
  height:9px;
  border:1.5px solid #5c91b0;
  border-radius:50%;
  bottom:25%;
  left:30%;
  opacity:0;
  z-index:1;
}
.hydrogen-chamber .bubble {
  border-color:var(--blue);
}
.b2 {
  left:55%;
  animation-delay:.8s!important;
  width:7px;
  height:7px;
}
.b3 {
  left:70%;
  animation-delay:1.5s!important;
}
.b4 {
  left:40%;
  animation-delay:2.2s!important;
  width:6px;
  height:6px;
}
.b5 {
  left:20%;
  animation-delay:1s!important;
}
.is-powered .bubble {
  animation:bubble-rise 3s infinite ease-in;
}
.is-powered .proton {
  animation:proton-flow 2.5s infinite linear;
}
.is-powered .flow-arrow {
  opacity:1;
  color:var(--blue);
}
.is-powered .power-wire {
  border-color:var(--blue);
}
@keyframes bubble-rise {
  0% {
    transform:translateY(0);
    opacity:0;
  }
  15% {
    opacity:.8;
  }
  90% {
    opacity:.8;
  }
  100% {
    transform:translateY(-95px);
    opacity:0;
  }
}
@keyframes proton-flow {
  0% {
    transform:translateX(-12px);
    opacity:0;
  }
  20% {
    opacity:1;
  }
  80% {
    opacity:1;
  }
  100% {
    transform:translateX(16px);
    opacity:0;
  }
}
.experiment-caption {
  font-size:12px;
  text-align:center;
  min-height:44px;
  color:#425765;
  margin-bottom:20px;
}
.part-tabs {
  display:flex;
  gap:7px;
  border-top:1px solid #ced8df;
  padding-top:20px;
  flex-wrap:wrap;
}
.part-tabs button {
  border:1px solid #bdcbd6;
  background:transparent;
  font-size:12px;
  border-radius:6px;
  padding:9px 13px;
  min-height:40px;
}
.part-tabs button[aria-pressed=true] {
  background:var(--ink);
  border-color:var(--ink);
  color:white;
}
.part-detail {
  padding-top:16px;
  min-height:106px;
}
.part-detail h3 {
  font-size:14px;
  margin-bottom:8px;
}
.part-detail p {
  font-size:12px;
  color:#52646f;
}
.equation {
  margin-top:20px;
  background:#e9eddf;
  padding:15px;
  font-size:21px;
  color:var(--ink);
  font-family:Georgia,serif;
}
.equation span {
  display:block;
  font-size:11px;
  margin-top:5px;
  font-family:inherit;
}
.material-story {
  display:grid;
  grid-template-columns:.8fr 1fr;
  gap:30px;
  align-items:center;
  margin-bottom:24px;
}
.material-image {
  position:relative;
}
.material-image img {
  width:100%;
  aspect-ratio:.85;
  object-fit:cover;
  border-radius:9px;
}
.material-image>span {
  display:block;
  font-size:10px;
  color:var(--muted);
  padding-top:12px;
}
.material-copy article {
  display:flex;
  gap:14px;
  padding:15px 0;
}
.material-copy article>span {
  font-family:monospace;
  font-size:11px;
  color:var(--blue);
  padding-top:3px;
}
.material-copy h3 {
  font-size:15px;
  margin-bottom:8px;
}
.material-copy p {
  font-size:12px;
  color:var(--muted);
}
.quiz {
  display:grid;
  gap:13px;
  margin-bottom:35px;
}
.quiz-item {
  background:var(--white);
  border:1px solid var(--line);
  border-radius:10px;
  padding:21px;
}
.quiz-question {
  display:flex;
  gap:12px;
  font-size:14px;
  font-weight:650;
  line-height:1.8;
}
.quiz-question span {
  font-family:monospace;
  color:var(--blue);
  font-size:12px;
}
.quiz-options {
  display:flex;
  flex-wrap:wrap;
  gap:8px;
  margin-top:15px;
}
.quiz-options button {
  padding:10px 13px;
  border-radius:6px;
  border:1px solid #d5dcd4;
  background:transparent;
  min-height:42px;
  font-size:12px;
  text-align:left;
  line-height:1.5;
}
.quiz-options button:hover {
  background:#eff2e8;
}
.quiz-options button.correct {
  border-color:#5c8054;
  background:#e8f0df;
}
.quiz-options button.incorrect {
  border-color:#b77e53;
  background:#f8eee0;
}
.quiz-feedback {
  font-size:12px;
  margin-top:13px;
  line-height:1.8;
  color:#4e6351;
}
.quiz-feedback:empty {
  display:none;
}
.personal-note {
  border:1px solid #cbd2c6;
  border-radius:10px;
  padding:24px;
  background:#eef1e5;
}
.personal-note label {
  display:block;
  font-size:13px;
  font-weight:650;
  margin-bottom:14px;
}
textarea {
  width:100%;
  background:var(--white);
  border:1px solid #cbd2c6;
  border-radius:7px;
  resize:vertical;
  min-height:110px;
  padding:14px;
  font-size:13px;
  line-height:1.8;
  color:var(--ink);
}
textarea::placeholder {
  color:#7a8277;
}
.note-bottom {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:15px;
  margin-top:13px;
}
.note-bottom>span {
  font-size:10px;
  line-height:1.7;
  color:var(--muted);
}
.next-study {
  margin-top:48px;
}
.next-study .eyebrow {
  color:var(--blue);
  font-size:10px;
}
.next-study h3 {
  font-size:23px;
  letter-spacing:-.8px;
  margin:12px 0 20px;
}
.next-study ol {
  padding:0;
  list-style:none;
}
.next-study li {
  display:flex;
  align-items:center;
  padding:13px 0;
  border-bottom:1px solid var(--line);
  gap:15px;
  font-size:13px;
}
.next-study li>span {
  font-family:monospace;
  font-size:11px;
  color:var(--muted);
}
.next-study li b {
  font-size:10px;
  font-weight:500;
  color:var(--blue);
  margin-left:auto;
  background:#e9edfa;
  padding:5px 9px;
  border-radius:20px;
}
.next-study li.future {
  color:#737c7d;
}
.next-study li.future b {
  background:#e8eae2;
  color:#68736a;
}
.next-study>p {
  font-size:12px;
  color:var(--muted);
  margin-top:24px;
}
.page-footer {
  padding:40px 0 60px;
  display:grid;
  grid-template-columns:1fr auto;
  gap:20px;
  font-size:11px;
}
.page-footer .brand {
  font-size:15px;
}
.page-footer .element-mark {
  height:32px;
  width:30px;
  font-size:20px;
}
.page-footer>p {
  grid-row:2;
  color:var(--muted);
  font-size:11px;
}
.page-footer>a:last-of-type {
  grid-column:2;
  grid-row:1;
  align-self:center;
}
.page-footer small {
  grid-column:1/-1;
  font-size:9px;
  color:var(--muted);
}
dialog {
  border:1px solid var(--line);
  border-radius:15px;
  background:var(--white);
  padding:24px;
  width:min(720px,calc(100% - 30px));
  max-height:90vh;
  color:var(--ink);
}
dialog::backdrop {
  background:#142636b8;
  backdrop-filter:blur(5px);
}
.dialog-top {
  display:flex;
  justify-content:space-between;
  align-items:center;
  gap:15px;
  margin-bottom:18px;
}
.dialog-top h2 {
  font-size:17px;
}
.dialog-top button {
  background:var(--paper);
  padding:12px;
  border-radius:7px;
  white-space:nowrap;
}
.dialog-top+img {
  max-height:55vh;
  width:100%;
  object-fit:contain;
  background:white;
}
dialog>p {
  font-size:13px;
  margin-top:18px;
}
dialog>a {
  display:inline-block;
  font-size:11px;
  margin-top:15px;
}
.image-unavailable {
  position:relative;
}
.image-unavailable:after {
  content:"사진을 불러오지 못했어요. 아래 원본 링크로 확인해 주세요.";
  display:block;
  font-size:12px;
  padding:20px;
  color:var(--muted);
}
@media(min-width:1500px) {
  .hero {
    min-height:690px;
  }
  .photo-paper img {
    height:370px;
  }
}
@media(max-width:1100px) {
  .page-width {
    width:calc(100% - 60px);
  }
  .site-header {
    padding-inline:30px;
  }
  .learning-layout {
    grid-template-columns:170px minmax(0,1fr);
    gap:30px;
  }
  .hero {
    gap:25px;
    min-height:590px;
  }
  .hero h1 {
    font-size:46px;
  }
  .hero-footnote span {
    display:block;
    margin-left:0;
  }
  .hero .eyebrow {
    font-size:10px;
  }
  .photo-paper img {
    height:290px;
  }
  .photo-sticker {
    width:65px;
    height:65px;
  }
  .lesson h2 {
    font-size:32px;
  }
  .use-grid {
    gap:10px;
  }
  .use-grid article {
    padding:18px 13px;
  }
  .use-grid h3 {
    font-size:13px;
  }
  .photo-grid {
    gap:10px;
  }
  .photo-grid h3 {
    font-size:14px;
  }
  .material-story {
    gap:18px;
  }
  .material-copy article {
    padding:10px 0;
  }
  .material-copy h3 {
    font-size:13px;
  }
  .material-copy p {
    font-size:11px;
  }
  .study-nav nav a {
    font-size:12px;
    gap:10px;
    padding-inline:8px;
  }
}
@media(max-width:800px) {
  .page-width {
    width:calc(100% - 40px);
  }
  .site-header {
    height:76px;
    padding-inline:20px;
  }
  .brand {
    font-size:16px;
  }
  .brand small {
    font-size:8px;
  }
  .header-right {
    gap:14px;
  }
  .edition {
    display:none;
  }
  .header-right .text-link {
    font-size:11px;
  }
  .hero {
    grid-template-columns:1fr 1fr;
    gap:20px;
    padding-block:45px;
    min-height:500px;
  }
  .hero h1 {
    font-size:35px;
    letter-spacing:-2px;
  }
  .hero-intro {
    font-size:13px;
  }
  .hero .eyebrow {
    font-size:9px;
    letter-spacing:0;
  }
  .photo-paper {
    padding:12px;
  }
  .photo-paper img {
    height:220px;
  }
  .photo-label {
    font-size:10px;
  }
  .photo-label strong {
    font-size:12px;
  }
  .photo-sticker {
    width:54px;
    height:54px;
    font-size:12px;
    right:12px;
    bottom:15px;
  }
  .hero-figure>figcaption {
    font-size:9px;
    margin-left:0;
  }
  .learning-layout {
    display:block;
  }
  .study-nav {
    position:sticky;
    top:76px;
    z-index:20;
    background:var(--paper);
    padding:0;
    border-bottom:1px solid var(--line);
  }
  .study-nav>.eyebrow,.nav-progress,.nav-note {
    display:none;
  }
  .study-nav nav {
    flex-direction:row;
    overflow-x:auto;
    gap:2px;
    padding:10px 0;
  }
  .study-nav nav a {
    white-space:nowrap;
    font-size:11px;
    padding:10px;
    gap:6px;
  }
  .study-nav nav a span {
    font-size:9px;
  }
  .lesson {
    padding:45px 0;
    scroll-margin-top:145px;
  }
  .material-image img {
    aspect-ratio:1;
  }
  .hero-footnote {
    font-size:9px;
  }
  .lesson h2 {
    font-size:32px;
  }
  .section-intro {
    font-size:13px;
  }
}
@media(max-width:560px) {
  .page-width {
    width:calc(100% - 36px);
  }
  .site-header {
    padding-inline:18px;
  }
  .hero {
    grid-template-columns:1fr;
    padding-top:33px;
    gap:30px;
  }
  .hero h1 {
    font-size:42px;
    letter-spacing:-2.3px;
    margin:20px 0;
  }
  .hero .eyebrow {
    font-size:10px;
  }
  .hero-intro {
    font-size:14px;
  }
  .hero-footnote {
    margin-top:20px;
  }
  .hero-footnote span {
    display:inline;
    margin-left:7px;
  }
  .hero-figure {
    padding:0 12px 0 2px;
  }
  .photo-paper {
    padding:14px 20px;
  }
  .photo-paper img {
    height:250px;
  }
  .photo-sticker {
    width:65px;
    height:65px;
    font-size:14px;
    right:20px;
  }
  .photo-label {
    font-size:11px;
  }
  .photo-label strong {
    font-size:13px;
  }
  .hero-figure>figcaption {
    margin-top:20px;
  }
  .hero-copy>.button {
    font-size:13px;
    padding:13px 19px;
  }
  .study-nav nav a {
    padding:10px 9px;
  }
  .study-nav nav a span {
    display:none;
  }
  .photo-grid {
    grid-template-columns:1fr;
    gap:20px;
  }
  .photo-grid figure {
    display:grid;
    grid-template-columns:44% 1fr;
    gap:17px;
    align-items:center;
  }
  .image-button {
    aspect-ratio:1;
  }
  .photo-grid figcaption {
    padding:0;
  }
  .photo-grid h3 {
    font-size:15px;
    margin:7px 0;
  }
  .photo-grid p {
    font-size:12px;
  }
  .photo-grid figcaption a {
    font-size:9px;
    margin-top:8px;
  }
  .takeaway {
    padding:18px;
    gap:12px;
  }
  .takeaway p {
    font-size:12px;
  }
  .use-grid {
    grid-template-columns:1fr;
    gap:9px;
  }
  .use-grid article {
    display:grid;
    grid-template-columns:38px 1fr;
    column-gap:15px;
    padding:16px;
  }
  .use-symbol {
    grid-row:1/3;
    margin:0;
    align-self:center;
  }
  .use-grid h3 {
    font-size:14px;
    margin-bottom:3px;
  }
  .use-grid p {
    font-size:12px;
  }
  .use-grid p br {
    display:none;
  }
  .plain-explanation {
    font-size:13px;
  }
  .lesson h2 {
    font-size:31px;
  }
  .section-number {
    font-size:10px;
  }
  .experiment {
    padding:17px 12px;
  }
  .cell-diagram {
    height:270px;
    margin-top:20px;
  }
  .water-feed {
    left:0;
    font-size:9px;
    top:122px;
  }
  .water-feed span {
    font-size:15px;
    margin-left:0;
  }
  .chamber-label {
    font-size:9px;
  }
  .chamber-label strong {
    font-size:10px;
  }
  .gas-label {
    font-size:9px;
    gap:4px;
  }
  .gas-label>span {
    font-size:20px;
  }
  .oxygen-label {
    left:18%;
  }
  .hydrogen-label {
    left:62%;
  }
  .membrane {
    font-size:10px;
  }
  .proton {
    font-size:9px;
  }
  .power-wire span {
    font-size:8px;
    width:210px;
    top:35px;
  }
  .experiment-caption {
    font-size:11px;
    padding-inline:4px;
    margin-bottom:14px;
    min-height:40px;
  }
  .part-tabs {
    gap:5px;
  }
  .part-tabs button {
    font-size:11px;
    padding:8px 10px;
  }
  .part-detail {
    min-height:130px;
    padding-inline:3px;
  }
  .part-detail h3 {
    font-size:13px;
  }
  .part-detail p {
    font-size:12px;
  }
  .material-story {
    grid-template-columns:1fr;
  }
  .material-image img {
    aspect-ratio:1.6;
    object-position:center;
  }
  .material-copy h3 {
    font-size:15px;
  }
  .material-copy p {
    font-size:13px;
  }
  .material-copy article {
    padding:14px 0;
  }
  .quiz-item {
    padding:17px;
  }
  .quiz-question {
    font-size:13px;
    gap:10px;
  }
  .quiz-options {
    flex-direction:column;
    align-items:stretch;
  }
  .quiz-options button {
    font-size:12px;
  }
  .personal-note {
    padding:17px;
  }
  .personal-note label {
    font-size:12px;
  }
  .note-bottom {
    align-items:flex-start;
    flex-direction:column;
  }
  .note-bottom .button {
    align-self:flex-end;
  }
  .next-study h3 {
    font-size:21px;
  }
  .next-study li {
    font-size:12px;
    gap:10px;
  }
  .next-study li b {
    font-size:9px;
  }
  .page-footer {
    column-gap:10px;
  }
  .page-footer .brand {
    font-size:13px;
  }
  .page-footer>a:last-of-type {
    font-size:10px;
  }
  .dialog-top h2 {
    font-size:14px;
  }
  dialog {
    padding:18px;
  }
}
@media(prefers-reduced-motion:reduce) {
  :root {
    scroll-behavior:auto;
  }
  *,*:before,*:after {
    animation:none!important;
    transition:none!important;
  }
  .is-powered .bubble {
    opacity:.75;
  }
  .is-powered .b1 {
    transform:translateY(-20px);
  }
  .is-powered .b2 {
    transform:translateY(-60px);
  }
  .is-powered .b3 {
    transform:translateY(-85px);
  }
  .is-powered .proton {
    opacity:1;
  }
}
.lang-switch {
  display:inline-flex;
  border:1px solid #cbd0c7;
  border-radius:30px;
  overflow:hidden;
}
.lang-switch button {
  border:0;
  background:transparent;
  padding:7px 12px;
  font-size:12px;
  font-weight:600;
  line-height:1.2;
}
.lang-switch button+button {
  border-left:1px solid #cbd0c7;
}
.lang-switch button[aria-pressed="true"] {
  background:var(--ink);
  color:var(--paper);
}
.lang-switch button:focus-visible {
  outline:2px solid var(--blue);
  outline-offset:-3px;
}
html[lang="en"] body {
  overflow-wrap:anywhere;
}
html[lang="en"] .hero h1 {
  letter-spacing:-1.2px;
}
html[lang="en"] .layer-strip strong,html[lang="en"] .system-scale span {
  font-size:13px;
}
html[lang="en"] .system-scale small {
  max-width:120px;
}
[data-untranslated]::before {
  content:"한국어 원문 · ";
  font-size:10px;
  color:var(--muted);
  font-weight:500;
}
.legacy-body [lang="en"] {
  margin-top:40px;
  padding-top:24px;
  border-top:1px solid var(--line);
}
.legacy-body h2 {
  font-size:22px;
  margin-bottom:16px;
}
@media(max-width:800px) {
  .lang-switch button {
    padding:6px 9px;
    font-size:11px;
  }
  html[lang="en"] .hero h1 {
    font-size:30px;
    letter-spacing:-1px;
  }
}
@media(max-width:700px) {
  html[lang="en"] .layer-strip strong {
    font-size:11px;
  }
  html[lang="en"] .system-scale span {
    font-size:12px;
  }
}
@media(max-width:560px) {
  .site-header .brand>span:last-child {
    display:none;
  }
  .lang-switch button {
    padding:6px 8px;
  }
}

/* Top navigation shared by every page: flat row of pills, current page filled; scrolls sideways on narrow screens. */
.site-nav {
  display:flex;
  align-items:center;
  gap:8px;
  padding:10px 50px;
  border-bottom:1px solid var(--line);
  background:var(--paper);
  overflow-x:auto;
  white-space:nowrap;
  font-size:13px;
  scrollbar-width:none;
}
.site-nav::-webkit-scrollbar {
  display:none;
}
.site-nav a {
  flex:none;
  text-decoration:none;
  font-weight:600;
  color:var(--ink);
  padding:7px 13px;
  border:1px solid #cbd0c7;
  border-radius:30px;
}
.site-nav a:hover,.site-nav a:focus-visible {
  border-color:var(--ink);
}
.site-nav a[aria-current="page"] {
  background:var(--ink);
  color:var(--paper);
  border-color:var(--ink);
}
@media(max-width:1100px) {
  .site-nav {
    padding-inline:30px;
  }
}
@media(max-width:800px) {
  .site-nav {
    padding:8px 20px;
    gap:6px;
  }
}
@media(max-width:560px) {
  .site-nav {
    padding-inline:18px;
  }
}

/* Private supplier files on Google Drive (booth banner pages): a pill with the lock marker and a short note. */
.drive-links {
  display:flex;
  flex-wrap:wrap;
  gap:10px;
  margin-top:14px;
}
.drive-link {
  display:inline-flex;
  flex-wrap:wrap;
  align-items:center;
  gap:8px;
  max-width:100%;
  padding:8px 14px;
  border:1px solid var(--line);
  border-radius:999px;
  background:var(--white);
  font-size:13px;
  line-height:1.5;
  text-decoration:none;
  color:var(--ink);
}
.drive-link small {
  font-size:11px;
  color:var(--muted);
}
.drive-link:hover,.drive-link:focus-visible {
  border-color:var(--ink);
}