:root{color-scheme:dark;font-family:Arial,'Noto Sans KR','Malgun Gothic',sans-serif;--accent:#8cc9d5;--ink:#edf4f5;--muted:#9fb2b8;--line:#91aab43d;background:#182329;color:var(--ink)}*{box-sizing:border-box}body{margin:0;min-height:100dvh;background:radial-gradient(ellipse at 50% 25%,#31434c,transparent 65%),linear-gradient(155deg,#25363e,#151e24 80%);display:flex;flex-direction:column;overflow-x:hidden}.menu-top{height:64px;border-bottom:1px solid var(--line);display:flex;align-items:center;justify-content:space-between;padding:0 30px;background:#18272eaa}.menu-top a{font-size:14px;color:var(--accent);text-decoration:none;display:flex;gap:9px;align-items:center}.menu-top svg{width:25px;height:25px}.menu-top span{font-size:11px;color:#9bb0a7}.mode-screen{flex:1;width:100%;max-width:1120px;margin:auto;display:flex;flex-direction:column;justify-content:center;padding:60px 40px;position:relative}.menu-heading{text-align:center;margin-bottom:52px}.menu-heading .period{display:block;letter-spacing:4px;font-size:11px;color:#a2b9c2;margin-bottom:17px}.menu-heading h1{font-size:clamp(36px,5.5vw,64px);letter-spacing:-2px;color:#edf4f5;margin:0;font-weight:700;text-shadow:0 3px 15px #0b151c42}.menu-heading p{font-size:16px;letter-spacing:1px;color:#a6bac3;margin:17px 0 0}.mode-choices{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:18px;position:relative;z-index:1}.mode-choice{text-decoration:none;color:var(--ink);border:1px solid #89a7b466;border-radius:8px;background:linear-gradient(145deg,#344950c9,#1c2c34ed);min-height:255px;padding:30px 26px 26px;display:flex;flex-direction:column;align-items:center;text-align:center;box-shadow:0 14px 35px #091b2338;transition:transform .18s,border-color .18s}.mode-choice:hover,.mode-choice:focus-visible{border-color:var(--accent);background:linear-gradient(145deg,#3d5a63c9,#233e49ed);transform:translateY(-4px);outline:none}.mode-choice>svg{width:44px;height:44px;stroke:var(--accent);margin-bottom:19px}.mode-choice h2{font-size:24px;font-weight:500;margin:0 0 12px;letter-spacing:1px}.mode-choice p{font-size:13px;color:#a7bdc6;line-height:1.9;margin:0 0 23px}.mode-choice .enter{margin-top:auto;color:var(--accent);font-size:12px;border-top:1px solid var(--line);width:100%;padding-top:15px}.menu-note{margin:28px 0 0;font-size:11px;text-align:center;color:#8fa69e;line-height:1.7}.menu-footer{padding:14px 25px;text-align:center;color:#809990;font-size:10px}.menu-footer a{color:#b3c0a6;text-decoration:none}.classroom-choices{grid-template-columns:repeat(2,minmax(0,1fr));max-width:700px;width:100%;margin:0 auto}.classroom-choices .mode-choice{min-height:270px}.menu-decoration{position:absolute;left:-20%;right:-20%;height:180px;top:25%;opacity:.045;pointer-events:none;background:repeating-linear-gradient(90deg,transparent 0 27px,#c3e2eb 27px 58px,transparent 58px 66px);clip-path:polygon(0 100%,0 70%,8% 70%,8% 40%,12% 40%,12% 60%,19% 60%,19% 20%,23% 20%,23% 50%,31% 50%,31% 10%,35% 10%,35% 45%,41% 45%,41% 25%,48% 25%,48% 55%,55% 55%,55% 0,59% 0,59% 40%,66% 40%,66% 25%,72% 25%,72% 60%,80% 60%,80% 10%,84% 10%,84% 50%,90% 50%,90% 30%,96% 30%,96% 80%,100% 80%,100% 100%)}@media(max-width:760px){.menu-top{padding:0 18px;height:54px}.menu-top>span{font-size:10px}.mode-screen{padding:40px 22px}.menu-heading{margin-bottom:30px}.menu-heading p{font-size:13px;letter-spacing:.2px}.mode-choices{gap:10px}.mode-choice{min-height:240px;padding:24px 14px 20px}.mode-choice h2{font-size:21px}.mode-choice p{font-size:11px}.mode-choice>svg{width:36px;height:36px}.menu-decoration{height:150px}.menu-heading .period{font-size:10px}}@media(max-width:540px){.mode-screen{justify-content:flex-start;padding:40px 20px 20px}.menu-heading{margin-bottom:28px}.menu-heading h1{font-size:39px;letter-spacing:-1.5px}.menu-heading .period{font-size:9px;letter-spacing:2px}.mode-choices,.classroom-choices{grid-template-columns:1fr;gap:11px}.mode-choice,.classroom-choices .mode-choice{min-height:120px;padding:18px;display:grid;grid-template-columns:40px 1fr auto;grid-template-rows:auto auto;gap:5px 16px;text-align:left;align-items:center}.mode-choice>svg{grid-row:1/3;margin:0;width:34px;height:34px}.mode-choice h2{font-size:21px;margin:0}.mode-choice p{font-size:11px;margin:0;line-height:1.6;grid-row:2;grid-column:2}.mode-choice .enter{grid-row:1/3;grid-column:3;border:0;padding:0;font-size:11px;width:auto;max-width:65px;line-height:1.7;margin:0}.menu-note{font-size:10px;margin-top:20px}.menu-top>span{display:none}.menu-footer{padding:16px;font-size:9px}}

/* Menu layout; the captured backdrop remains visible while live scenes load. */
.home-menu{background:#18272e}.menu-backdrop{position:fixed;inset:0;z-index:0;overflow:hidden;pointer-events:none}.menu-backdrop>img{width:100%;height:100%;object-fit:cover;object-position:center}.menu-shade{position:absolute;inset:0;background:linear-gradient(180deg,#102129c9 0%,#1021296b 28%,#10212925 52%,#1021299e 75%,#102129f5 100%)}.home-menu .menu-top,.home-menu .mode-screen,.home-menu .menu-footer{position:relative;z-index:1}.home-menu .menu-top{background:#18272e80}.home-menu .mode-screen{min-height:calc(100dvh - 110px);padding:42px 40px 38px;justify-content:flex-start}.home-menu .menu-decoration{display:none}.home-menu .menu-heading{margin:0 0 32px;text-shadow:0 2px 16px #0a1924aa}.home-menu .menu-heading .period{color:#d2e6eb;letter-spacing:5px}.home-menu .menu-heading p{color:#deebee}.home-menu .mode-choices{margin-top:auto;gap:14px}.home-menu .mode-choice{min-height:175px;padding:20px 22px 16px;background:linear-gradient(145deg,#2c434cec,#1c3038f5);box-shadow:0 8px 28px #07141c45;backdrop-filter:blur(8px);border-color:#8ca9b577}.home-menu .mode-choice>svg{width:32px;height:32px;margin-bottom:11px}.home-menu .mode-choice h2{font-size:22px;margin-bottom:8px}.home-menu .mode-choice p{font-size:12px;line-height:1.7;margin-bottom:13px}.home-menu .mode-choice .enter{padding-top:10px}.home-menu .menu-note{color:#c1d4dd;margin-top:18px}.home-menu .menu-footer{color:#96b0bd;background:#14242d70}.era-caption{position:absolute;top:40%;display:flex;flex-direction:column;gap:5px;color:#f1f6ed;text-shadow:0 2px 14px #102129c9}.era-caption strong{font-size:clamp(30px,4vw,54px);font-weight:400;letter-spacing:2px}.era-caption span{font-size:12px;letter-spacing:.8px}.era-early{left:5%}.era-modern{right:5%;text-align:right;color:#d8eff4}@media(max-width:760px){.home-menu .mode-screen{padding:30px 22px 28px;min-height:calc(100dvh - 100px)}.home-menu .mode-choice{padding:18px 13px 15px}.era-caption{top:38%}.era-caption span{font-size:10px}.era-early{left:4%}.era-modern{right:4%}}@media(max-width:540px){.home-menu .mode-screen{padding:28px 20px 20px;min-height:calc(100dvh - 100px)}.home-menu .menu-heading{margin-bottom:140px}.home-menu .menu-heading h1{font-size:42px}.home-menu .mode-choices{gap:9px}.home-menu .mode-choice{min-height:98px;padding:15px 14px;background:#203740ed}.home-menu .mode-choice>svg{margin:0;width:30px;height:30px}.home-menu .mode-choice h2{font-size:20px;margin:0}.home-menu .mode-choice p{font-size:10px;margin:0}.home-menu .mode-choice .enter{font-size:10px;padding:0}.home-menu .menu-note{font-size:10px;margin-top:15px}.era-caption{top:29%;gap:2px}.era-caption strong{font-size:29px}.era-caption span{font-size:9px}.menu-shade{background:linear-gradient(180deg,#102129c9 0%,#10212944 35%,#1021293d 50%,#102129dc 77%,#102129f5 100%)}}@media(max-height:640px) and (min-width:541px){.home-menu .mode-screen{padding:20px 32px}.home-menu .menu-heading{margin-bottom:15px}.home-menu .menu-heading h1{font-size:42px}.home-menu .menu-heading .period{margin-bottom:8px}.home-menu .menu-heading p{margin-top:9px}.home-menu .mode-choice{min-height:155px;padding:12px 18px}.home-menu .mode-choice>svg{display:none}.home-menu .menu-note{margin-top:10px}.era-caption{top:38%}.era-caption strong{font-size:30px}}

/* Live era scenes meet in a feathered transition. */
.era-world{position:absolute;top:50%;width:var(--era-size);height:var(--era-size);transform:translateY(-50%);opacity:0;transition:opacity .7s;background:#d7e3e5}.era-world.ready{opacity:1}.era-world canvas{display:block;pointer-events:none}/* Two square scenes cover the viewport with a narrow shared fade at the center. */
.menu-backdrop{--era-size:max(100dvh,55vw)}
.era-world-early{left:0;z-index:1;mask-image:linear-gradient(to right,#000 46vw,transparent 54vw)}
.era-world-modern{right:0}
@media(orientation:portrait){
 .menu-backdrop{--era-size:max(100vw,55dvh)}
 .era-world{left:50%;right:auto;transform:translateX(-50%)}
 .era-world-early{top:0;mask-image:linear-gradient(to bottom,#000 46dvh,transparent 54dvh)}
 .era-world-modern{top:auto;bottom:0}
 .home-menu .era-caption.era-early{top:12%}
 .home-menu .era-caption.era-modern{top:auto;bottom:9%}
}
.live-menu-ready .menu-backdrop>img{opacity:0;transition:opacity .7s}.menu-shade,.era-caption{z-index:2}.menu-backdrop{background:#b7bca3}@media(prefers-reduced-motion:reduce){.era-world,.live-menu-ready .menu-backdrop>img{transition:none}}
.menu-3d-notice{position:absolute;top:52%;left:20%;right:20%;padding:10px;font-size:12px;color:#e6f0f4;background:#203642bd;text-align:center}.era-world.ready canvas{width:100%!important;height:100%!important}.era-world .map-label{display:none}.era-world-early{background:#b8d3df}.era-world-modern{background:#081426}
.home-menu .menu-backdrop>img{display:none}.menu-backdrop{background:linear-gradient(90deg,#9bb9c7 0%,#7894a5 38%,#263c52 60%,#081426 100%)}

.home-menu .menu-shade{background:linear-gradient(180deg,#10212988,transparent 23%,transparent 63%,#10212988),linear-gradient(90deg,transparent 35%,#08142633 65%)}.home-menu .era-world-early{filter:none}.home-menu .era-world-modern{filter:none}.home-menu .era-early{color:#fff9df;text-shadow:0 2px 8px #152732}.home-menu .menu-heading{pointer-events:none}.home-menu .era-caption{top:38%}
.menu-scene-layer{position:absolute;inset:0;overflow:hidden}.menu-gpu-layer{opacity:0;transition:opacity .5s}.menu-gpu-layer.visible{opacity:1}.home-menu .menu-backdrop{isolation:isolate}.home-menu .era-world{opacity:1}.home-menu .menu-backdrop .era-world-early{background:#c6d7dd}.home-menu .menu-backdrop .era-world-modern{background:#071222}.home-menu .era-caption{top:37%}.home-menu .era-caption span{font-size:13px}

/* Give the two eras distinct light while preserving the moving city detail. */
.home-menu .era-world-early .menu-scene-layer{filter:sepia(.24) saturate(.92) contrast(1.08)}
.home-menu .era-world-modern .menu-scene-layer{filter:saturate(1.24) brightness(1.14)}
.home-menu .menu-shade{
 background:
  linear-gradient(180deg,#07141fe8 0%,#07141fa6 17%,transparent 42%,#07141f17 54%,#07141fbb 82%,#07141ff0 100%),
  radial-gradient(ellipse at 26% 41%,#f5b9732e,transparent 43%),
  radial-gradient(ellipse at 75% 46%,#46a9df24,transparent 46%),
  radial-gradient(ellipse at center,transparent 40%,#07121d72 100%);
}
.home-menu .menu-heading h1{
 font-family:Georgia,"Noto Serif KR","Batang",serif;
 font-weight:800;letter-spacing:.035em;
 color:#fff3da;text-shadow:0 3px 12px #080e19,0 10px 35px #101a2c;
}
.home-menu .menu-heading .period{display:flex;align-items:center;justify-content:center;gap:13px;color:#eed0a0}
.home-menu .menu-heading .period::before,.home-menu .menu-heading .period::after{
 content:"";width:clamp(20px,7vw,76px);height:1px;background:linear-gradient(90deg,transparent,#e7c699);
}
.home-menu .menu-heading .period::after{transform:scaleX(-1)}
.home-menu .era-caption{top:43%;gap:2px}
.home-menu .era-caption strong{font-family:Georgia,serif;font-size:clamp(34px,5.7vw,85px);line-height:1;text-shadow:0 3px 18px #081321}
.home-menu .era-caption span{border-block-start:1px solid currentColor;padding-top:7px;font-size:clamp(10px,1.2vw,14px);letter-spacing:.04em}
.home-menu .era-modern{color:#bde8fb}
@media(orientation:portrait){
 .home-menu .menu-shade{
  background:linear-gradient(180deg,#07141fe8 0%,#07141f9c 16%,transparent 34%,#0b1c2c35 53%,#07141fa8 75%,#07141fee 100%),
   radial-gradient(ellipse at 34% 30%,#f5b97322,transparent 45%),
   radial-gradient(ellipse at 69% 61%,#46a9df22,transparent 45%);
 }
 .home-menu .era-caption.era-early{top:33%}
 .home-menu .era-caption.era-modern{top:53%;bottom:auto}
}
@media(max-height:640px){
 .home-menu .era-caption strong{font-size:clamp(26px,5vw,44px)}
}
@media(orientation:portrait) and (max-height:660px){
 .home-menu .era-caption span{display:none}
 .home-menu .era-caption.era-early{top:36%}
 .home-menu .era-caption.era-modern{top:48%}
}