:root {
  color-scheme: light;
  --paper: #fffdf8;
  --white: #ffffff;
  --ink: #202b3b;
  --muted: #627084;
  --blue: #2d6ae5;
  --blue-deep: #204eae;
  --orange: #ff812d;
  --teal: #007e88;
  --line: #dce1e8;
  --sky: #eaf5ff;
  --math-wash: #edf5ff;
  --physics-wash: #fff2e4;
  --chemistry-wash: #e5f6f1;
  --atom-blue: #aad3fb;
  --success: #e6f5e9;
  --success-ink: #20623b;
  --review: #fff1e4;
  --review-ink: #85401a;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans", "Thonburi", "Lao Sangam MN", "Noto Sans Thai", "Noto Sans Lao", system-ui, sans-serif;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 32px; }
body { margin: 0; background: var(--paper); color: var(--ink); font-family: var(--font); font-size: 16px; line-height: 1.65; -webkit-font-smoothing: antialiased; }
button, input { font: inherit; }
button, a, summary { -webkit-tap-highlight-color: transparent; }
button, a { touch-action: manipulation; }
button { cursor: pointer; }
a { color: inherit; }
svg { display: block; flex-shrink: 0; }
img { display: block; max-width: 100%; height: auto; }
[hidden] { display: none !important; }
:focus-visible { outline: 3px solid var(--blue); outline-offset: 5px; }
h1, h2, h3, p { margin: 0; }
h1, h2, h3 { font-weight: 600; }
h2 { font-size: clamp(30px, 3.1vw, 44px); line-height: 1.24; letter-spacing: -.035em; text-wrap: balance; }
.container { width: min(1240px, calc(100% - 96px)); margin-inline: auto; }
.skip-link { position: fixed; top: 12px; left: 16px; z-index: 20; padding: 10px 18px; background: var(--white); transform: translateY(-160%); }
.skip-link:focus { transform: none; }
.site-header { min-height: 104px; display: flex; align-items: center; gap: 60px; }
.brand { display: inline-flex; align-items: center; gap: 9px; text-decoration: none; font-size: 32px; font-weight: 700; letter-spacing: -.055em; line-height: 1.2; white-space: nowrap; }
.brand-mark { width: 35px; height: 35px; color: var(--blue); }
.brand-suffix { color: var(--blue); }
.desktop-nav { display: flex; align-items: center; gap: 34px; }
.desktop-nav a { padding-block: 10px; text-decoration: none; font-size: 15px; }
.desktop-nav a:hover { color: var(--blue); }
.header-actions { display: flex; align-items: center; gap: 24px; margin-left: auto; }
.button { display: inline-flex; justify-content: center; align-items: center; gap: 18px; min-height: 54px; padding: 12px 26px; border: 1px solid var(--blue); border-radius: 9px; color: var(--white); background: var(--blue); box-shadow: 0 3px 0 var(--blue-deep); text-decoration: none; font-size: 16px; font-weight: 600; line-height: 1.5; transition: background 150ms, transform 150ms, box-shadow 150ms; }
.button svg { width: 24px; height: 24px; }
.button:hover { background: var(--blue-deep); }
.button:active { transform: translateY(2px); box-shadow: 0 1px 0 var(--blue-deep); }
.button-outline { min-height: 43px; padding: 8px 19px; background: transparent; color: var(--blue); box-shadow: none; border-radius: 6px; font-size: 14px; font-weight: 500; }
.button-outline:hover { color: var(--white); }
.language-menu { position: relative; }
.language-menu > summary { list-style: none; display: flex; align-items: center; justify-content: space-between; gap: 13px; min-height: 43px; padding: 8px 13px; border: 1px solid var(--line); border-radius: 6px; cursor: pointer; font-size: 14px; white-space: nowrap; }
summary::-webkit-details-marker { display: none; }
.language-menu svg { width: 18px; height: 18px; }
.language-menu nav { position: absolute; right: 0; top: calc(100% + 8px); z-index: 10; min-width: 174px; padding: 7px; background: var(--white); border: 1px solid var(--line); border-radius: 10px; box-shadow: 0 12px 32px #202b3b12; }
.language-menu nav a { display: block; padding: 9px 13px; border-radius: 6px; font-size: 15px; text-decoration: none; }
.language-menu nav a:hover, .language-menu [aria-current] { color: var(--blue); background: var(--math-wash); }
.hero { display: grid; grid-template-columns: 1.36fr 1fr; align-items: center; min-height: 560px; padding-top: 35px; padding-bottom: 52px; }
.hero-copy { position: relative; z-index: 1; }
h1 { font-size: clamp(44px, 4.45vw, 64px); line-height: 1.14; letter-spacing: -.05em; text-wrap: balance; }
h1 span { display: block; }
.hero-accent { color: var(--blue); }
.hero-intro { max-width: 610px; margin-top: 30px; font-size: 18px; line-height: 1.8; }
.hero-actions { display: flex; align-items: center; flex-wrap: wrap; gap: 28px; margin-top: 30px; }
.text-link { color: var(--blue); font-size: 15px; font-weight: 600; text-underline-offset: 4px; }
.text-link:hover { color: var(--blue-deep); }
.development-note { max-width: 590px; margin-top: 27px; color: var(--muted); font-size: 13px; }
.hero-media { width: 116%; margin-left: -6%; }
.subjects { padding-top: 54px; padding-bottom: 58px; }
.subject-list { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 48px; margin-top: 40px; }
.subject { --subject-color: var(--blue); display: flex; flex-direction: column; }
.subject-1 { --subject-color: var(--orange); }
.subject-2 { --subject-color: var(--teal); }
.subject-rule { display: flex; align-items: center; gap: 13px; color: var(--subject-color); font-size: 17px; font-weight: 600; }
.subject-rule::after { content: ""; flex: 1; height: 2px; background: var(--subject-color); }
.subject h3 { font-size: 30px; letter-spacing: -.035em; line-height: 1.4; margin-top: 12px; }
.subject > p { margin-top: 10px; font-size: 16px; line-height: 1.75; }
.subject-diagram { margin-top: auto; padding-top: 18px; }
.subject-diagram svg { width: 230px; height: 110px; max-width: 100%; }
.subject .subject-topics { margin-top: 12px; color: var(--muted); font-size: 12px; line-height: 1.7; }
.method { display: grid; grid-template-columns: 1fr 1fr; gap: 94px; align-items: start; padding-block: 86px 100px; }
.method-copy { padding-top: 18px; }
.method h2 span { display: block; }
.method-copy > p { margin-top: 25px; max-width: 470px; font-size: 17px; line-height: 1.8; }
.steps { list-style: none; margin: 0; padding: 0; }
.steps li { display: flex; gap: 29px; align-items: start; padding-block: 21px 25px; border-bottom: 1px solid var(--line); }
.steps li:last-child { border-bottom: 0; }
.step-number { color: var(--orange); font-size: 44px; font-weight: 500; line-height: 1.3; letter-spacing: -.06em; }
.steps h3 { font-size: 20px; line-height: 1.5; }
.steps p { margin-top: 4px; color: var(--muted); font-size: 15px; }
.sample-band { background: var(--sky); padding-block: 64px; }
.sample-layout { display: grid; grid-template-columns: .9fr 1.1fr; align-items: center; gap: 84px; }
.sample-copy p { max-width: 440px; margin-top: 25px; font-size: 17px; line-height: 1.85; }
.sample-card { min-width: 0; padding: 23px 30px 30px; border-radius: 20px; background: var(--white); }
.subject-tabs { display: none; grid-template-columns: repeat(3, minmax(0, 1fr)); border-bottom: 1px solid var(--line); margin-bottom: 23px; }
.js .subject-tabs { display: grid; }
.sample-form > button { display: none; }
.js .sample-form > button { display: flex; }
.subject-tabs button { background: transparent; color: var(--muted); border: none; border-bottom: 3px solid transparent; margin-bottom: -1px; padding: 11px 5px 13px; font-size: 14px; font-weight: 600; line-height: 1.5; overflow-wrap: anywhere; }
.subject-tabs [aria-selected="true"] { color: var(--blue); border-bottom-color: var(--blue); }
.sample-label { font-size: 12px; color: var(--muted); margin-bottom: 10px; }
fieldset { padding: 0; border: 0; margin: 0; min-width: 0; }
legend { padding: 0; width: 100%; font-size: 18px; line-height: 1.65; font-weight: 400; }
.answers { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 12px; margin-top: 20px; }
.answer { position: relative; display: flex; gap: 11px; align-items: center; min-height: 50px; padding: 10px 14px; border: 1px solid var(--line); border-radius: 8px; cursor: pointer; font-size: 16px; }
.answer input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.answer:has(input:focus-visible) { outline: 3px solid var(--blue); outline-offset: 3px; }
.answer:has(input:checked) { border-color: var(--blue); background: var(--math-wash); }
.answer-key { color: var(--muted); font-size: 11px; }
.answer.is-correct { background: var(--success); border-color: var(--success-ink); }
.answer.is-incorrect { background: var(--review); border-color: var(--review-ink); }
.answer:has(input:disabled) { cursor: default; }
.check-button, .retry-button { width: 100%; min-height: 47px; margin-top: 21px; box-shadow: none; border-radius: 7px; font-size: 14px; }
.answer-error { margin-top: 13px; font-size: 14px; color: var(--review-ink); }
.answer-feedback { margin-top: 19px; padding: 15px 17px; background: var(--review); border-radius: 8px; color: var(--ink); font-size: 14px; line-height: 1.8; }
.answer-feedback[data-result="correct"] { background: var(--success); }
.answer-feedback strong { display: block; font-weight: 600; margin-bottom: 5px; }
.no-script { font-size: 13px; padding-top: 18px; }
.faq { padding-block: 69px 60px; }
.faq-list { margin-top: 27px; border-top: 1px solid var(--line); }
.faq-list details { border-bottom: 1px solid var(--line); }
.faq-list summary { display: flex; align-items: center; justify-content: space-between; gap: 24px; list-style: none; min-height: 68px; padding-block: 18px; cursor: pointer; font-size: 16px; }
.faq-list summary svg { width: 20px; height: 20px; transition: transform 180ms; }
.faq-list details[open] summary svg { transform: rotate(180deg); }
.faq-list details > p { max-width: 900px; padding-block: 0 23px; color: var(--muted); font-size: 15px; line-height: 1.9; }
.contact-section { display: grid; grid-template-columns: 1.5fr 1fr; align-items: center; gap: 64px; border-top: 1px solid var(--line); padding-block: 48px 58px; margin-bottom: 35px; }
.contact-section h2 { font-size: 34px; }
.contact-section p { max-width: 720px; margin-top: 18px; color: var(--muted); font-size: 16px; line-height: 1.85; }
.contact-action { display: flex; flex-direction: column; align-items: flex-end; gap: 18px; }
.contact-address { color: var(--muted); font-size: 14px; text-underline-offset: 4px; }
.site-footer { padding-block: 0 30px; }
.footer-top { display: flex; justify-content: space-between; gap: 32px; align-items: center; }
.footer-top > div { display: flex; align-items: center; gap: 24px; }
.footer-brand { color: var(--blue); font-size: 25px; letter-spacing: -.035em; }
.footer-line { padding-left: 24px; border-left: 1px solid var(--line); font-size: 12px; color: var(--muted); }
.official-link { display: inline-flex; align-items: center; gap: 16px; color: var(--blue); font-size: 12px; text-decoration: none; }
.official-link:hover { text-decoration: underline; text-underline-offset: 4px; }
.official-link svg { width: 18px; height: 18px; }
.footer-bottom { display: flex; justify-content: space-between; align-items: baseline; gap: 20px; padding-top: 23px; color: var(--muted); font-size: 12px; }
address { display: flex; gap: 14px; flex-wrap: wrap; align-items: baseline; font-style: normal; }
address a { text-underline-offset: 3px; }
:lang(th), :lang(lo) { letter-spacing: 0; }
html:lang(th) h1, html:lang(lo) h1 { font-size: clamp(36px, 3.7vw, 53px); line-height: 1.5; }
html:lang(th) h2, html:lang(lo) h2 { line-height: 1.55; }
html:lang(th) .subject h3, html:lang(lo) .subject h3 { line-height: 1.6; }
@media (min-width: 1500px) { .hero { min-height: 590px; } }
@media (max-width: 1100px) {
  .container { width: calc(100% - 64px); }
  .site-header { gap: 34px; }
  .desktop-nav { gap: 23px; }
  .header-actions { gap: 15px; }
  .hero { grid-template-columns: 1.2fr 1fr; min-height: 540px; }
  h1 { font-size: 48px; }
  .hero-intro { font-size: 16px; }
  .hero-actions { gap: 23px; }
  .subject-list { gap: 32px; }
  .subject h3 { font-size: 26px; }
  .method, .sample-layout { gap: 48px; }
  .sample-card { padding-inline: 22px; }
  .footer-top > div { align-items: start; flex-direction: column; gap: 12px; }
  .footer-line { border: 0; padding: 0; }
}
@media (max-width: 800px) {
  .container { width: calc(100% - 40px); }
  .site-header { min-height: 84px; gap: 20px; }
  .desktop-nav, .header-cta { display: none; }
  .brand { font-size: 29px; }
  .brand-mark { width: 31px; height: 31px; }
  .hero { display: flex; flex-direction: column; align-items: stretch; min-height: auto; padding-top: 44px; padding-bottom: 25px; }
  h1 { font-size: clamp(38px, 6.8vw, 56px); }
  .hero-intro { font-size: 17px; max-width: 620px; margin-top: 24px; }
  .hero-actions { margin-top: 25px; }
  .hero-media { width: min(100%, 500px); margin: 22px auto -10px; }
  .subjects { padding-top: 32px; padding-bottom: 10px; }
  .subject-list { gap: 27px; margin-top: 30px; }
  .subject h3 { font-size: 23px; }
  .subject > p { font-size: 14px; }
  .subject-diagram svg { height: 90px; }
  .subject-topics { font-size: 11px; }
  .method { gap: 38px; padding-block: 60px; }
  .method-copy > p, .sample-copy p { font-size: 16px; }
  .steps li { gap: 18px; }
  .step-number { font-size: 36px; }
  .steps h3 { font-size: 18px; }
  .steps p { font-size: 14px; }
  .sample-layout { grid-template-columns: 1fr; gap: 28px; }
  .sample-copy p { max-width: 650px; margin-top: 16px; }
  .sample-card { width: 100%; max-width: 620px; }
  .sample-band { padding-block: 43px; }
  .faq { padding-block: 47px; }
  .footer-top, .footer-bottom { align-items: start; }
  .footer-bottom { flex-direction: column-reverse; gap: 18px; }
  html:lang(th) h1, html:lang(lo) h1 { font-size: clamp(33px, 5.8vw, 48px); }
}
@media (max-width: 560px) {
  .container { width: calc(100% - 40px); }
  .hero { padding-top: 27px; }
  h1 { font-size: clamp(37px, 9vw, 49px); }
  .hero-intro { font-size: 16px; line-height: 1.85; }
  .hero-actions { align-items: start; flex-direction: column; gap: 22px; }
  .button { min-height: 52px; padding-inline: 22px; }
  .development-note { font-size: 12px; margin-top: 23px; }
  .hero-media { margin-top: 12px; }
  h2 { font-size: 30px; }
  .subject-list { grid-template-columns: 1fr; gap: 33px; }
  .subject { position: relative; padding-right: 0; }
  .subject h3 { font-size: 28px; }
  .subject > p { font-size: 16px; max-width: 420px; }
  .subject-diagram { padding-top: 12px; }
  .subject-diagram svg { width: 180px; height: 86px; }
  .subject .subject-topics { margin-top: 5px; font-size: 12px; }
  .method { grid-template-columns: 1fr; gap: 19px; padding-top: 56px; }
  .method-copy { padding-top: 0; }
  .method-copy > p { margin-top: 19px; }
  .steps li { gap: 23px; padding-block: 21px; }
  .sample-card { padding: 15px 17px 21px; border-radius: 16px; }
  .subject-tabs { margin-bottom: 20px; }
  .subject-tabs button { font-size: 12px; padding-inline: 3px; }
  legend { font-size: 17px; }
  .answers { gap: 10px; }
  .answer { padding-inline: 11px; gap: 8px; font-size: 16px; }
  .check-button, .retry-button { min-height: 47px; }
  .faq-list summary { font-size: 15px; }
  .contact-section { grid-template-columns: 1fr; gap: 27px; padding-block: 34px 39px; margin-bottom: 25px; }
  .contact-section h2 { font-size: 28px; }
  .contact-action { align-items: flex-start; }
  .footer-top { flex-direction: column; gap: 22px; }
  .official-link { min-height: 44px; }
  address { gap: 6px 12px; line-height: 1.8; }
  address span:first-child { flex-basis: 100%; }
  html:lang(th) h1, html:lang(lo) h1 { font-size: 33px; line-height: 1.55; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition: none !important; }
}