*{box-sizing:border-box}:root{--ink:#143342;--muted:#607683;--blue:#075d87;--blue2:#1689bd;--teal:#22a9a7;--bg:#f4f8fa;--line:#d5e2e8;--soft:#eaf5f8;--warm:#fff7d8;--good:#16734a;--goodbg:#e8f7ef;--bad:#ac2a20;--badbg:#fff0ed}html,body{margin:0;font-family:system-ui,-apple-system,"Segoe UI",sans-serif;background:var(--bg);color:var(--ink)}button,input{font:inherit}button{cursor:pointer}.hidden{display:none!important}header{position:sticky;top:0;z-index:5;display:grid;grid-template-columns:auto 1fr auto;align-items:center;gap:14px;padding:14px clamp(14px,4vw,48px);background:#fffffff2;border-bottom:1px solid var(--line)}header small,.eyebrow{color:var(--blue);font-size:.72rem;font-weight:850;text-transform:uppercase;letter-spacing:.08em}h1{font-size:1.42rem;margin:1px 0}main{max-width:1080px;margin:auto;padding:28px clamp(14px,3vw,34px) 80px}.hero{display:grid;grid-template-columns:1fr auto;align-items:center;gap:24px;padding:34px;background:linear-gradient(135deg,#e7f7fa,#fff7d5);border:1px solid var(--line);border-radius:26px}.hero h2{font-size:clamp(1.55rem,3vw,2.25rem);line-height:1.15;margin:14px 0}.hero p{font-size:1.05rem;line-height:1.55}.symbol{width:150px;height:150px;display:grid;place-items:center;border-radius:50%;background:white;color:var(--blue);font:800 3.2rem Cambria,serif}.pill{display:inline-flex;padding:6px 11px;border-radius:999px;background:#ddf2f2;color:#116c6a;font-size:.78rem;font-weight:850}.stats{display:grid;grid-template-columns:repeat(3,1fr);gap:13px;margin:22px 0 36px}.stats div{padding:18px;background:white;border:1px solid var(--line);border-radius:18px;text-align:center}.stats b{display:block;color:var(--blue);font-size:1.7rem}.stats span{font-size:.8rem;color:var(--muted)}#chapters{display:grid;gap:15px}.chapter{display:grid;grid-template-columns:auto 1fr auto;gap:18px;align-items:center;padding:21px;background:white;border:1px solid var(--line);border-radius:20px}.chapter.locked{opacity:.55}.num{width:52px;height:52px;display:grid;place-items:center;border-radius:16px;background:var(--soft);color:var(--blue);font-weight:900;font-size:1.25rem}.chapter h3{margin:0 0 5px}.chapter p{margin:0;color:var(--muted);line-height:1.45}.status{font-size:.78rem;font-weight:850;color:var(--muted)}.primary,.secondary,.plain,.icon,.danger{border:0;border-radius:13px;font-weight:800}.primary{padding:13px 20px;background:var(--blue);color:white}.secondary{padding:13px 18px;background:var(--soft);color:var(--blue)}.plain{padding:9px 12px;background:transparent;color:var(--blue)}.icon{width:42px;height:42px;background:var(--soft);color:var(--blue);font-size:1.3rem}.danger{padding:12px 16px;background:var(--badbg);color:var(--bad)}.topline{display:flex;gap:10px;align-items:center;color:var(--muted);font-weight:750}.progress{height:11px;background:#dce8ed;border-radius:999px;overflow:hidden;margin-top:11px}.progress div{height:100%;width:0;background:linear-gradient(90deg,var(--teal),var(--blue2));transition:.3s}.percent{text-align:right;font-size:.85rem;font-weight:850;margin:5px 0 12px}article{max-width:830px;margin:auto;padding:clamp(22px,5vw,45px);background:white;border:1px solid var(--line);border-radius:26px}.toolbar{display:flex;justify-content:space-between;align-items:center}.toolbar>span{color:var(--teal);font-size:.78rem;font-weight:900;text-transform:uppercase;letter-spacing:.08em}article h2{font-size:clamp(1.65rem,4vw,2.5rem);margin:26px 0 18px}.text{font-size:clamp(1.05rem,2.3vw,1.28rem);line-height:1.65}.visual{margin:25px 0;padding:24px;border-radius:20px;background:#f9fcfd;border:1px solid var(--line);text-align:center}.math{font-family:Cambria,serif;font-size:clamp(2rem,7vw,4.2rem);font-weight:750}.smallmath{font-family:Cambria,serif;font-size:clamp(1.35rem,4vw,2.1rem);font-weight:750}.flow{display:flex;flex-direction:column;align-items:center;gap:11px}.arrow{color:var(--teal);font-size:2rem}.table{border-collapse:collapse;margin:auto;font-size:1.08rem}.table th,.table td{border:2px solid #bfd1d9;padding:11px 15px;text-align:center}.table th{background:var(--soft);color:var(--blue)}.focus{background:#fff3bf!important}.choices{display:grid;gap:11px;margin-top:24px}.choice{width:100%;padding:16px;text-align:left;border:2px solid var(--line);border-radius:14px;background:white;font-weight:720}.choice.selected{border-color:var(--blue2);background:#edf8fb}.number{width:min(100%,360px);padding:15px;border:2px solid #bfd1d9;border-radius:13px;font-size:1.18rem;margin-top:24px}.multi{display:grid;grid-template-columns:repeat(5,1fr);gap:8px;margin-top:24px}.multi input{width:100%;padding:12px 4px;text-align:center;border:2px solid #bfd1d9;border-radius:10px}.feedback{margin-top:18px;padding:15px;border-radius:14px;line-height:1.55}.feedback.good{background:var(--goodbg);color:var(--good)}.feedback.bad{background:var(--badbg);color:var(--bad)}.feedback.hint{background:var(--warm);color:#755800}.actions{display:flex;gap:11px;flex-wrap:wrap;margin-top:22px}dialog{width:min(92vw,520px);border:1px solid var(--line);border-radius:20px;padding:0}dialog form{padding:22px}.dialoghead{display:flex;justify-content:space-between;align-items:center}dialog label{display:flex;justify-content:space-between;padding:22px 0;border-bottom:1px solid var(--line)}footer{display:flex;justify-content:space-between;padding:17px clamp(14px,4vw,48px);background:white;border-top:1px solid var(--line);color:var(--muted);font-size:.8rem}@media(max-width:700px){.hero{grid-template-columns:1fr}.symbol{display:none}.stats{grid-template-columns:1fr}.chapter{grid-template-columns:auto 1fr}.chapter button{grid-column:1/-1;width:100%}article{padding:21px}header small{display:none}footer{flex-direction:column;gap:8px}}
.book-calculation{width:min(100%,520px);margin:auto;padding:18px 22px;background:#e5f0f1;font-family:Cambria,serif;font-size:clamp(1.15rem,3vw,1.55rem)}.equation-line{display:grid;grid-template-columns:1fr 90px;align-items:baseline;min-height:38px}.equation-line>span:first-child{text-align:center}.equation-line>span:last-child{text-align:left}.root-lines{margin-top:5px}.root-lines>div{display:grid;grid-template-columns:1fr 70px 1fr;gap:8px}.root-lines span:first-child{text-align:right}.root-lines span:last-child{text-align:left}.solution-set{margin-top:8px;text-align:center}@media(max-width:700px){.book-calculation{padding:15px 10px}.equation-line{grid-template-columns:1fr 70px}.root-lines>div{grid-template-columns:1fr 48px 1fr;gap:4px}}
.equivalence-helper,.equivalence-addition{color:#d8645b}.equivalence-note{color:var(--muted);font-family:system-ui,-apple-system,"Segoe UI",sans-serif;font-size:.92rem}
.equivalence-operation{width:min(100%,360px);font-family:Cambria,serif;font-size:clamp(1.35rem,4vw,2.1rem);font-weight:750}
.equivalence-detail{display:flex;align-items:center;justify-content:center;gap:16px;width:100%}.equivalence-detail .equivalence-note{max-width:190px;text-align:left;font-size:.78rem;line-height:1.35}
@media(max-width:520px){.equivalence-detail{gap:8px}.equivalence-detail .smallmath{font-size:1.05rem}.equivalence-detail .equivalence-note{max-width:145px;font-size:.7rem}}
.equivalence-stack{display:grid;gap:11px;width:100%;font-family:Cambria,serif;font-size:clamp(1.35rem,4vw,2.1rem);font-weight:750}.equivalence-row{display:grid;grid-template-columns:minmax(60px,1fr) 24px minmax(110px,1fr) 78px minmax(0,230px);align-items:center;column-gap:6px}.equivalence-row>span:first-child{text-align:right}.equivalence-row>span:nth-child(2){text-align:center}.equivalence-row>span:nth-child(3),.equivalence-row>span:nth-child(4){text-align:left}.equivalence-row .equivalence-note{font-family:system-ui,-apple-system,"Segoe UI",sans-serif;font-size:.92rem;font-weight:400;line-height:1.4;text-align:left;color:var(--muted)}
@media(max-width:520px){.equivalence-stack{font-size:1rem}.equivalence-row{grid-template-columns:45px 16px 88px 45px minmax(80px,1fr);column-gap:3px}.equivalence-row .equivalence-note{font-size:.72rem}}
.ordering{display:grid;gap:10px;margin-top:24px}.ordering-step{display:grid;grid-template-columns:34px 1fr auto;align-items:center;gap:10px;padding:10px 12px;border:2px solid var(--line);border-radius:14px;background:#fff}.ordering-number{display:grid;place-items:center;width:28px;height:28px;border-radius:50%;background:var(--soft);color:var(--blue);font-weight:850}.ordering-text{font-family:Cambria,serif;font-size:1.2rem;font-weight:700}.ordering-controls{display:flex;gap:5px}.ordering-move{width:38px;height:38px;border:0;border-radius:9px;background:var(--soft);color:var(--blue);font-size:1.1rem;font-weight:900}.ordering-move:disabled{opacity:.25;cursor:default}
.missing-slot{display:inline-grid;place-items:center;min-width:30px;min-height:28px;padding:1px 7px;border:2px solid #6f9eb4;border-radius:7px;background:#bfd9e5;color:#064f73;font-family:system-ui,-apple-system,"Segoe UI",sans-serif;font-size:.9em;font-weight:900;line-height:1}
.test-card-navigation{display:flex;justify-content:space-between;align-items:center;gap:14px;margin-top:30px;padding-top:18px;border-top:2px dashed var(--line)}.test-card-navigation>span{color:var(--muted);font-size:.78rem;font-weight:850;text-transform:uppercase;letter-spacing:.06em}.test-card-navigation>div{display:flex;gap:10px;flex-wrap:wrap}.test-card-navigation button{padding:10px 14px}.test-card-navigation button:disabled{opacity:.4;cursor:default}@media(max-width:600px){.test-card-navigation{align-items:stretch;flex-direction:column}.test-card-navigation>div{display:grid;grid-template-columns:1fr 1fr}.test-card-navigation button{width:100%;padding:10px 8px;font-size:.86rem}}
.multi.wide{grid-template-columns:repeat(var(--answer-columns),minmax(52px,1fr));overflow-x:auto;padding-bottom:5px}
.table td.table-answer-cell{padding:4px}.table-answer-input{display:block;width:48px;min-width:42px;padding:8px 3px;border:2px solid #9fbfce;border-radius:7px;background:#fff;text-align:center;font-size:1rem}.table-answer-input:focus{border-color:var(--blue2);outline:2px solid #ccecf7;outline-offset:1px}
.important-instruction{margin:18px 0;padding:15px 17px;border:2px solid #e5b326;border-left-width:7px;border-radius:12px;background:#fff4bf;color:#624b00;line-height:1.5}
.equation-answer{width:min(100%,560px);font-family:Cambria,serif;font-size:1.35rem}

/* iPad and Safari layout */
html{-webkit-text-size-adjust:100%}
button,.choice,input{touch-action:manipulation}
.visual{max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch}
.visual>svg{display:block;margin-inline:auto}
.table{white-space:nowrap}

@media (min-width:701px) and (max-width:1366px){
  header{padding-top:max(12px,env(safe-area-inset-top));padding-left:max(22px,env(safe-area-inset-left));padding-right:max(22px,env(safe-area-inset-right))}
  main{max-width:1240px;padding:22px max(22px,env(safe-area-inset-right)) 64px max(22px,env(safe-area-inset-left))}
  #learn article{width:100%;max-width:1120px;padding:clamp(26px,3.5vw,38px)}
  article h2{margin:22px 0 15px}
  .text{font-size:clamp(1.05rem,1.8vw,1.22rem)}
  .visual{margin:20px 0;padding:20px}
  .choice{min-height:52px;padding:14px 16px}
  .primary,.secondary,.plain,.danger{min-height:44px}
  .number{min-height:50px;font-size:1.1rem}
  .table-answer-input{min-height:44px;font-size:1rem}
  dialog{max-height:calc(100dvh - 40px);overflow:auto;-webkit-overflow-scrolling:touch}
}

@media (min-width:980px) and (max-width:1366px) and (orientation:landscape){
  #learn article.has-visual{display:grid;grid-template-columns:minmax(300px,.82fr) minmax(470px,1.18fr);column-gap:32px;align-items:start}
  #learn article.has-visual .toolbar,
  #learn article.has-visual>h2,
  #learn article.has-visual .test-card-navigation{grid-column:1/-1}
  #learn article.has-visual .text{grid-column:1;grid-row:3}
  #learn article.has-visual .visual{grid-column:2;grid-row:3/span 4;margin:0;align-self:start}
  #learn article.has-visual #interaction{grid-column:1;grid-row:4}
  #learn article.has-visual #feedback{grid-column:1;grid-row:5}
  #learn article.has-visual>.actions{grid-column:1;grid-row:6}
  #learn article.has-visual .test-card-navigation{grid-row:7;margin-top:24px}
  #learn article.has-visual .choices{margin-top:18px}
  #learn article.has-visual .number{margin-top:18px}
  #learn article.has-visual .visual .table th,
  #learn article.has-visual .visual .table td{padding:9px 12px}
}

@media (display-mode:standalone){
  footer{padding-bottom:max(17px,env(safe-area-inset-bottom))}
}

.topic-help-panel{margin-top:22px;padding-top:18px;border-top:1px dashed var(--line)}
.topic-help-buttons{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:10px}
.topic-help-button{height:auto;min-height:52px;padding:11px 13px;line-height:1.3}
.topic-help-answers{display:grid;gap:10px;margin-top:12px}
.topic-help-answer{padding:15px 17px;border-radius:14px;background:var(--warm);color:#755800;line-height:1.5}
.topic-help-answer ol{margin:9px 0 0;padding-left:24px}
.topic-help-answer li+li{margin-top:6px}
.topic-help-answer small{display:block;margin-top:10px;font-weight:700}
@media(max-width:700px){.topic-help-buttons{grid-template-columns:1fr}}
@media (min-width:980px) and (max-width:1366px) and (orientation:landscape){
  #learn article.has-visual #topicHelpPanel{grid-column:1;grid-row:6}
  #learn article.has-visual>.actions{grid-row:7}
  #learn article.has-visual .test-card-navigation{grid-row:8}
}