:root{--navy:#12263f;--navy2:#1c3557;--blue:#356fe3;--light:#eef4ff;--text:#223247;--muted:#65758a;--line:#dfE7f0;--white:#fff;--success:#127960}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:#f5f7fb;color:var(--text);font:15px/1.65 system-ui,"Malgun Gothic",Arial,sans-serif}a{color:inherit;text-decoration:none}button{font:inherit;cursor:pointer}a:focus-visible,button:focus-visible,input:focus-visible{outline:3px solid #ffbd69;outline-offset:2px}.frame{width:min(1170px,calc(100% - 36px));margin:auto}
.topbar{background:#fff;border-bottom:1px solid #e2e8f1}.topbar-inner{min-height:77px;display:flex;align-items:center;justify-content:space-between;gap:20px}.brand{display:flex;align-items:center;gap:11px;font-weight:900;letter-spacing:.025em}.brand small{display:block;font-size:10px;letter-spacing:.12em;font-weight:800;color:#66829f}.brandmark{display:grid;place-items:center;border-radius:12px;background:#2058c0;color:white;width:42px;height:42px;font-size:23px}.topbar nav{display:flex;flex-wrap:wrap;gap:18px;font-size:13px;font-weight:700;color:#50657e}.topbar nav a:hover{color:var(--blue)}
.hero{display:grid;grid-template-columns:minmax(0,1.15fr) minmax(320px,.85fr);gap:48px;align-items:center;background:linear-gradient(121deg,#132641,#233d60 76%,#2a4a73);color:white;padding:66px 54px;margin-top:24px;border-radius:18px;box-shadow:0 20px 44px #1a345225}.kicker{font-size:11px;font-weight:900;letter-spacing:.17em;color:#6597eb}.hero .kicker{color:#9cc7ff}.hero h1{font-size:clamp(34px,4.5vw,53px);line-height:1.24;margin:17px 0 20px;letter-spacing:-.06em}.hero h1 em{color:#91bfff;font-style:normal}.hero p{max-width:560px;color:#cfdaea;margin:0 0 25px}.hero-actions,.hero-tags{display:flex;gap:10px;flex-wrap:wrap}.main-btn,.ghost-btn{padding:12px 18px;border-radius:8px;font-weight:800;font-size:14px}.main-btn{background:#4c83fa;color:white}.ghost-btn{border:1px solid #8097b5;color:white}.hero-tags{margin-top:24px}.hero-tags span{border:1px solid #ffffff29;color:#d4e2f5;font-size:11px;padding:5px 10px;border-radius:50px}.hero-board{background:#0d1c30;border:1px solid #425875;border-radius:12px;overflow:hidden;box-shadow:0 16px 30px #04121f3e}.board-head{padding:15px 19px;display:flex;align-items:center;justify-content:space-between;border-bottom:1px solid #344a63;font-size:11px;letter-spacing:.12em;color:#9bb8d7;font-weight:800}.board-head strong{font-size:17px;color:white;letter-spacing:0}.board-row{display:flex;align-items:center;gap:13px;padding:10px 18px;border-bottom:1px solid #243a55}.board-row span{font-size:11px;color:#8daee0}.board-row b{flex:1;font-size:13px;font-weight:650}.board-row em{font-style:normal;color:#84c5ff;font-size:12px}.hero-board>small{display:block;padding:12px 18px;color:#aac0d8;font-size:10px}
.notice{margin:22px 0 27px;padding:15px 19px;border:1px solid #eed7ad;border-radius:9px;background:#fff9eb;color:#6f5335;font-size:13px}.notice a{font-weight:800;text-decoration:underline}.study-layout{display:grid;grid-template-columns:265px minmax(0,1fr);align-items:start;gap:23px}.rail,.lesson{background:white;border:1px solid var(--line);border-radius:13px;overflow:hidden}.rail{position:sticky;top:12px}.rail-inner{padding:23px 15px}.rail-label{font-size:10px;font-weight:900;letter-spacing:.16em;color:#5f8dcc}.rail h2{font-size:24px;line-height:1.25;margin:9px 0}.rail p{margin:8px 0 21px;font-size:12px;color:var(--muted)}.progress{padding:13px;background:#f1f5fb;border-radius:8px;margin-bottom:15px}.progress strong{font-size:13px}.progress-track{margin:8px 0;background:#d8e4f3;height:6px;border-radius:20px;overflow:hidden}.progress-track span{display:block;height:100%;width:0;background:var(--blue);transition:width .2s}.progress small{font-size:10px;color:var(--muted)}#stageNav{display:grid;gap:6px}#stageNav button{border:1px solid transparent;text-align:left;background:white;padding:12px 10px;border-radius:8px;display:flex;align-items:flex-start;gap:10px;width:100%;color:#405369}#stageNav button:hover{background:#f4f8ff}#stageNav button.active{background:#eaf2ff;border-color:#b8cdf5;color:#1c4fa6}#stageNav button .num{font-size:11px;font-weight:850;padding-top:2px;white-space:nowrap;color:#7392bf}#stageNav button b{display:block;font-size:12px;line-height:1.45}#stageNav button small{font-size:10px;color:#7e8fa5}#stageNav button .tick{margin-left:auto;color:var(--success);font-weight:900}.rail-links{border-top:1px solid var(--line);padding-top:15px;margin-top:17px;display:grid;gap:7px}.rail-links a{font-weight:700;color:#315d95;font-size:12px;padding:6px 0}
.lesson-head{padding:28px 31px;display:flex;gap:20px;align-items:flex-start;justify-content:space-between;background:linear-gradient(104deg,#fcfdff,#f0f6ff);border-bottom:1px solid var(--line)}.lesson-head h2{font-size:27px;margin:5px 0;letter-spacing:-.04em}.lesson-head p{color:#5d728b;margin:0;font-size:14px}.minute-chip{flex:none;padding:10px 14px;background:#e8efff;color:#2155a2;border-radius:9px}.minute-chip small{display:block;font-size:11px}.minute-chip strong{font-size:13px}.lesson-body{padding:26px 30px 30px}.lead{margin:0 0 22px;color:#566b83;font-size:14px}.panel{background:white;border:1px solid #e4eaf2;border-radius:10px;padding:21px 23px;margin-bottom:16px}.panel h3{font-size:16px;margin:0 0 12px;letter-spacing:-.02em}.duo{display:grid;grid-template-columns:1fr 1fr;gap:16px}.duo .panel{min-width:0}.pills{display:flex;flex-wrap:wrap;gap:6px}.pills span{font-size:11px;color:#366295;border-radius:60px;background:#edf5ff;padding:5px 8px}.help{font-size:12px;color:#64758a;margin:10px 0 0}.help a{color:#2559b6;text-decoration:underline}.file-label{font-family:Consolas,monospace;background:#152840;color:white;padding:13px;border-radius:7px;font-size:13px;word-break:break-word}.section-heading{display:flex;gap:12px;align-items:center;justify-content:space-between}.section-heading h3{margin:0}.section-heading span{font-size:11px;color:#8e9caf}.tasks{margin:14px 0 0;padding-left:23px}.tasks li{margin-bottom:11px;line-height:1.72}.code{margin:16px 0 0;background:#102036;color:#dbeeff;padding:20px;border-radius:9px;white-space:pre;overflow:auto;font:12px/1.65 ui-monospace,SFMono-Regular,Consolas,monospace;max-height:420px}.meaning{margin-top:14px;padding:13px 16px;border-left:3px solid #5e93f1;background:#eff5ff;color:#345775;font-size:13px}.small-btn{border:1px solid #bfd1ec;background:#f3f7ff;color:#305a9a;border-radius:6px;padding:6px 11px;font-size:12px;font-weight:700}.copy-info{font-size:11px;color:#39704e}.troubleshoot{border-color:#f0d9c5;background:#fffaf6}.troubleshoot h3{color:#8a5131}.troubleshoot p{margin:7px 0 0;font-size:13px}.checklist{display:grid;gap:11px}.checklist label{display:flex;align-items:flex-start;gap:11px;background:#f6f9fc;padding:11px 13px;border-radius:8px;font-size:13px}.checklist input{margin-top:4px;width:17px;height:17px;accent-color:#2775c7}.nav-buttons{margin-top:23px;display:flex;justify-content:space-between;gap:12px}.nav-buttons button{padding:10px 19px;border-radius:7px;background:white;border:1px solid #d9e2ef;font-weight:800}.nav-buttons button.primary{border:0;background:#326ddd;color:white}.nav-buttons button:disabled{opacity:.45;cursor:default}
.finish-area{display:flex;justify-content:space-between;gap:28px;background:white;border:1px solid var(--line);border-radius:13px;padding:27px 30px;margin:27px 0 46px}.finish-area h2{font-size:21px;margin:5px 0}.finish-area p{max-width:620px;color:#69809a;margin:0;font-size:13px}.finish-links{flex:0 0 245px;display:grid;gap:8px;align-content:center}.finish-links a,.finish-links button{border:1px solid #c8d6ec;background:#f7faff;padding:9px 11px;border-radius:6px;text-align:center;font-weight:800;color:#315c9a;font-size:12px}.footer{background:#152740;color:#9eb4d1;padding:24px 0;font-size:11px}
@media(max-width:930px){.hero{gap:28px;padding:38px 30px;grid-template-columns:1fr}.hero-board{max-width:590px}.study-layout{grid-template-columns:1fr}.rail{position:static}.rail-inner{display:block}.rail h2 br{display:none}#stageNav{display:grid;grid-template-columns:repeat(3,minmax(0,1fr))}#stageNav button{min-width:0}.rail-links{display:flex;flex-wrap:wrap;gap:14px}.duo{grid-template-columns:1fr 1fr}}
@media(max-width:600px){.frame{width:calc(100% - 24px)}.topbar-inner{padding:13px 0;align-items:flex-start;flex-direction:column}.topbar nav{gap:12px;font-size:11px}.hero{margin-top:12px;padding:30px 19px;border-radius:10px}.hero h1{font-size:35px}.hero-actions a{width:100%;text-align:center}.hero-tags span{font-size:10px}.board-head strong{font-size:14px}.notice{font-size:12px;padding:13px}.rail-inner{padding:17px}#stageNav{grid-template-columns:repeat(2,minmax(0,1fr))}#stageNav button{padding:8px}.lesson-head{padding:21px 17px;flex-direction:column}.lesson-head h2{font-size:23px}.lesson-body{padding:16px 12px}.panel{padding:17px 14px}.duo{grid-template-columns:1fr;gap:0}.code{padding:14px;font-size:11px}.tasks li{font-size:13px}.finish-area{flex-direction:column;padding:21px 17px}.finish-links{flex:none}}
@media print{.topbar,.rail,.hero-actions,.hero-board,.finish-links,.nav-buttons,.small-btn{display:none!important}.hero{display:block;background:white;color:black;padding:0;box-shadow:none}.hero h1 em{color:inherit}.study-layout{display:block}.lesson{border:0}.lesson-body{padding:0}.panel{break-inside:avoid}.footer{display:none}}

.target-demo{display:grid;grid-template-columns:minmax(0,.83fr) minmax(0,1.17fr);gap:24px;align-items:center;margin:0 0 27px;padding:21px;background:white;border:1px solid #e1e8f2;border-radius:12px}.target-demo h2{font-size:22px;letter-spacing:-.045em;line-height:1.4;margin:8px 0}.target-demo p{color:#65758a;font-size:13px}.target-demo a{color:#245bb1;text-decoration:underline;font-weight:850;font-size:13px}.target-demo img{width:100%;height:auto;display:block;border:1px solid #dce5f1;border-radius:7px}@media(max-width:650px){.target-demo{grid-template-columns:1fr;padding:15px}.target-demo h2{font-size:20px}}