:root {
  --navy:#071f3d;
  --navy-2:#123b69;
  --gold:#ffca05;
  --ink:#142033;
  --muted:#5f6b7a;
  --paper:#f5f7fa;
  --white:#fff;
  --line:#d9e0e8;
  --success:#176b45;
  --danger:#a72b32;
  --radius:14px;
  --shadow:0 18px 45px rgba(7,31,61,.10);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--paper);color:var(--ink);font-family:"Segoe UI",Arial,sans-serif;line-height:1.55}
button,input{font:inherit}
button{cursor:pointer}
.skip-link{position:fixed;left:16px;top:-60px;background:var(--gold);color:var(--navy);padding:10px 16px;z-index:20;font-weight:700}
.skip-link:focus{top:12px}
.site-header{min-height:82px;display:flex;align-items:center;justify-content:space-between;padding:14px clamp(20px,5vw,72px);background:var(--navy);color:var(--white);border-bottom:5px solid var(--gold)}
.brand{display:flex;align-items:center;gap:13px;line-height:1.15}
.brand-mark{display:grid;place-items:center;width:46px;height:46px;border:2px solid var(--gold);border-radius:50%;font:700 28px Georgia;color:var(--gold)}
.brand strong,.brand small{display:block}.brand small{margin-top:5px;color:#c8d4e2}
.text-button{border:1px solid #7791ad;background:transparent;color:white;border-radius:8px;padding:10px 14px;min-height:44px}
main{min-height:calc(100vh - 150px)}
.intro{padding:clamp(58px,9vw,116px) clamp(20px,8vw,130px);background:linear-gradient(115deg,var(--navy) 0 54%,#0d3157 54% 100%);color:white;position:relative;overflow:hidden}
.intro:after{content:"∞";position:absolute;right:5%;top:-90px;font:700 clamp(240px,35vw,520px) Georgia;color:rgba(255,202,5,.08);line-height:1;pointer-events:none}
.intro>*{position:relative;z-index:1}
.eyebrow{margin:0 0 8px;text-transform:uppercase;letter-spacing:.15em;font-size:.74rem;font-weight:800;color:#587089}
.intro .eyebrow{color:var(--gold)}
h1{font-family:Georgia,serif;font-size:clamp(2.5rem,5.2vw,5.2rem);line-height:1.02;letter-spacing:-.035em;margin:0;max-width:900px}
.lead{font-size:clamp(1.05rem,1.8vw,1.3rem);max-width:720px;color:#dbe4ee;margin:25px 0 38px}
.identity-panel{display:grid;grid-template-columns:repeat(2,minmax(180px,1fr));gap:16px 18px;align-items:start;background:white;color:var(--ink);padding:22px;border-radius:var(--radius);max-width:980px;box-shadow:var(--shadow)}
.identity-panel>div{display:flex;flex-direction:column}
.identity-panel>.field-wide{grid-column:1/-1}
.identity-panel>button{grid-column:1/-1;justify-self:start;margin-top:6px}
.conditional-field[hidden]{display:none}
label{display:block;font-weight:700;margin-bottom:7px}
input,select{width:100%;min-height:48px;border:1px solid #aab6c4;border-radius:8px;padding:10px 12px;background:white;color:var(--ink)}
select{appearance:auto}
input:focus,select:focus,button:focus-visible{outline:3px solid rgba(255,202,5,.75);outline-offset:2px}
input[aria-invalid="true"],select[aria-invalid="true"]{border-color:var(--danger)}
small{display:block;color:var(--muted);margin-top:5px}
.field-error{display:block;color:var(--danger);font-size:.85rem;font-weight:700;margin-top:6px;min-height:0}
.field-error:empty{margin-top:0}
.primary-button,.secondary-button{min-height:48px;padding:11px 20px;border-radius:8px;font-weight:800;border:2px solid var(--navy)}
.primary-button{background:var(--gold);color:var(--navy)}
.primary-button:hover{background:#ffda4a}
.secondary-button{background:white;color:var(--navy)}
.secondary-button:hover{background:#eaf0f7}
.workspace{display:grid;grid-template-columns:minmax(240px,330px) minmax(0,1fr);gap:clamp(25px,5vw,72px);max-width:1450px;margin:auto;padding:clamp(28px,5vw,70px)}
.workspace[hidden]{display:none}
.case-rail{align-self:start;position:sticky;top:24px;background:var(--navy);color:white;border-radius:var(--radius);padding:28px;box-shadow:var(--shadow);border-top:6px solid var(--gold)}
.case-rail .eyebrow{color:var(--gold)}
.mode-badge{display:inline-flex;align-items:center;min-height:32px;margin:0 0 15px;padding:6px 11px;border:1px solid var(--gold);border-radius:999px;color:var(--gold);font-size:.76rem;font-weight:800;letter-spacing:.08em;text-transform:uppercase}
.mode-badge.practice{border-color:#9fc1e2;color:#d8e9f8}
.case-number{display:flex;align-items:baseline;gap:9px;border-bottom:1px solid #41617f;padding-bottom:20px}.case-number strong{font:700 4.5rem/1 Georgia;color:var(--gold)}.case-number small{color:#afc1d2}
.case-meta{margin:10px 0 0}.case-meta div{padding:16px 0;border-bottom:1px solid #294a68}.case-meta dt{color:#9db1c4;font-size:.78rem;text-transform:uppercase;letter-spacing:.1em;font-weight:700}.case-meta dd{margin:5px 0 0;font-weight:650}
.assignment-note{font-size:.85rem;color:#cbd8e5;margin:20px 0 0}
.quiz-column{display:grid;gap:22px}
.step{background:white;border:1px solid var(--line);border-radius:var(--radius);padding:clamp(20px,3vw,34px);box-shadow:0 8px 24px rgba(12,40,69,.05)}
.step-heading{display:flex;gap:16px;align-items:start;margin-bottom:24px}.step-heading>span{display:grid;place-items:center;width:42px;height:42px;border-radius:50%;background:var(--navy);color:var(--gold);font-weight:800;flex:none}.step-heading h2{font:700 clamp(1.35rem,2vw,1.75rem) Georgia;margin:0;color:var(--navy)}
.phase-grid{border:0;padding:0;margin:0;display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:10px}
.phase-choice{position:relative}.phase-choice input{position:absolute;opacity:0;width:1px;height:1px}.phase-choice label{display:grid;place-items:center;text-align:center;min-height:68px;padding:10px;border:2px solid var(--line);border-radius:10px;margin:0;font-weight:650;background:#fbfcfe}.phase-choice input:checked+label{border-color:var(--navy);background:#edf3fa;box-shadow:inset 0 -4px 0 var(--gold)}.phase-choice input:focus-visible+label{outline:3px solid rgba(255,202,5,.75);outline-offset:2px}
.property-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:16px}.property-field{background:#f7f9fc;border:1px solid var(--line);border-radius:10px;padding:16px}.property-field label{font-family:Georgia,serif;font-size:1.25rem}.input-row{display:grid;grid-template-columns:1fr auto;align-items:center;gap:8px}.unit{font-weight:700;color:var(--navy);min-width:75px}
.helper{color:var(--muted);margin:10px 0 0;font-size:.92rem}
.hint{margin-top:15px;padding:14px 16px;background:#fff8d9;border-radius:8px;color:#574400}
.diagram-grid{display:grid;grid-template-columns:1fr 1fr;gap:18px}.diagram{margin:0;border:1px solid var(--line);border-radius:10px;padding:15px;background:#fbfcfe}.diagram figcaption{font-family:Georgia,serif;font-weight:700;color:var(--navy);margin-bottom:8px}.plot{display:block;width:100%;height:260px;background:white;border-radius:6px;touch-action:manipulation;cursor:crosshair}
.plot:focus-visible{outline:3px solid rgba(255,202,5,.85);outline-offset:3px}
.schematic-note{margin:8px 0 0;color:var(--muted);font-size:.78rem;font-style:italic}
.diagram-status{margin:6px 0 0;color:var(--navy-2);font-size:.85rem;font-weight:650;min-height:1.3em}
.diagram-controls{display:flex;flex-wrap:wrap;gap:12px 16px;align-items:end;margin-top:14px;padding-top:14px;border-top:1px solid var(--line)}
.diagram-controls .small-button{min-height:44px;padding:9px 16px}
.region-select{display:flex;flex-direction:column;flex:1 1 220px;min-width:200px}
.region-select label{font-weight:600;font-size:.85rem;margin-bottom:6px}
.region-select select{min-height:44px}
.stronger-guide{margin-top:18px}
.stronger-guide button:disabled{opacity:.6}
.actions{display:flex;justify-content:flex-end;gap:12px;flex-wrap:wrap}.results{border-radius:var(--radius);padding:24px;background:white;border:2px solid var(--navy)}.results.success{border-color:var(--success)}.results h2{margin-top:0;color:var(--navy)}.result-list{padding-left:20px}.correct{color:var(--success);font-weight:700}.incorrect{color:var(--danger);font-weight:700}
.practice-panel{background:var(--navy);color:white;border-radius:var(--radius);padding:clamp(22px,3vw,34px);border-top:6px solid var(--gold);box-shadow:var(--shadow)}.practice-panel .eyebrow{color:var(--gold)}.practice-panel h2{margin:0 0 10px;font:700 clamp(1.35rem,2vw,1.75rem) Georgia;color:white}.practice-panel p:not(.eyebrow){max-width:720px;color:#d5e0eb}.practice-actions{display:flex;gap:12px;flex-wrap:wrap;margin-top:20px}.practice-panel .secondary-button{border-color:white}.workspace.is-submitted .step,.workspace.is-submitted .actions{display:none}button:disabled,input:disabled{cursor:not-allowed;opacity:.65}
footer{display:flex;justify-content:space-between;gap:20px;padding:22px clamp(20px,5vw,72px);background:#06172d;color:#aebdcd;font-size:.85rem}
.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}
@media(max-width:900px){.identity-panel{grid-template-columns:1fr}.workspace{grid-template-columns:1fr}.case-rail{position:static}.case-meta{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}.case-meta div{border:0}.phase-grid{grid-template-columns:repeat(2,1fr)}}
@media(max-width:600px){.site-header{padding:12px 16px}.brand small{display:none}.intro{padding:48px 20px}.workspace{padding:22px 14px}.case-meta,.property-grid,.diagram-grid{grid-template-columns:1fr}.phase-grid{grid-template-columns:1fr}.actions>*,.practice-actions>*{width:100%}footer{flex-direction:column}.plot{height:230px}.diagram-controls{flex-direction:column;align-items:stretch}.diagram-controls .small-button{width:100%}.region-select{min-width:0}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{transition:none!important;animation:none!important}}