:root{--ink: #171717;--body: #4d4d4d;--muted: #888888;--hair: #ebebeb;--page: #ffffff;--card: #fafafa;--green: #4a9457;--green-deep: #2c6537;--green-soft: #e2f0e5;--r-sm: 6px;--r-md: 8px;--r-lg: 12px;--font: Geist, Inter, -apple-system, "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;--mono: "Geist Mono", ui-monospace, SFMono-Regular, Menlo, monospace;--ring-hover: inset 0 0 0 1px rgba(0, 0, 0, .16);--shadow-card: inset 0 0 0 1px rgba(0, 0, 0, .08), 0 1px 1px rgba(0, 0, 0, .02), 0 2px 2px rgba(0, 0, 0, .04);--shadow-card-hover: inset 0 0 0 1px rgba(0, 0, 0, .16), 0 2px 2px rgba(0, 0, 0, .04), 0 8px 8px -8px rgba(0, 0, 0, .04);--topbar-h: 56px}*{box-sizing:border-box}html,body,#root{min-height:100%}body{margin:0;background:var(--page);color:var(--body);font-family:var(--font);font-size:15px;line-height:1.65;-webkit-font-smoothing:antialiased}h1,h2,h3{color:var(--ink);font-weight:600;letter-spacing:-.3px;line-height:1.3;margin:0}h1{font-size:20px;letter-spacing:-.5px}h2{font-size:16px}h3{font-size:14px}a{color:var(--green-deep);text-decoration:none}a:hover{text-decoration:underline}:focus-visible{outline:2px solid var(--green);outline-offset:2px}.eyebrow{font-size:11px;font-weight:500;letter-spacing:.6px;text-transform:uppercase;color:var(--body)}.boot{padding:20vh 24px;text-align:center;color:var(--body)}.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;height:36px;padding:0 16px;border:0;border-radius:var(--r-md);background:var(--ink);color:#fff;font:500 14px var(--font);cursor:pointer;text-decoration:none;transition:background .15s,box-shadow .15s}.btn:hover{background:#000;text-decoration:none}.btn:disabled{opacity:.45;cursor:not-allowed}.btn-quiet{background:var(--page);color:var(--ink);box-shadow:var(--shadow-card)}.btn-quiet:hover{background:var(--card);box-shadow:var(--shadow-card-hover)}.card{background:var(--card);border-radius:var(--r-lg);box-shadow:var(--shadow-card);padding:20px}.badge{display:inline-flex;align-items:center;height:22px;padding:0 8px;border-radius:var(--r-sm);font-size:12px;font-weight:500;color:var(--body);background:var(--page);box-shadow:inset 0 0 0 1px var(--hair)}.badge-ready{color:var(--green-deep);background:var(--green-soft);box-shadow:none}.topbar{position:sticky;top:0;z-index:20;height:var(--topbar-h);display:flex;align-items:center;justify-content:space-between;padding:0 24px;background:var(--page);border-bottom:1px solid var(--hair)}.brand{font-weight:600;color:var(--ink);letter-spacing:-.3px;white-space:nowrap}.brand:hover{text-decoration:none}.brand span{color:var(--muted);font-weight:400}.topbar-user{display:flex;gap:16px;align-items:center;min-width:0;font-size:14px;color:var(--body)}.topbar-user span{min-width:0;max-width:40vw;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.page{min-height:calc(100vh - var(--topbar-h))}.container{max-width:1040px;margin:0 auto;padding:40px 24px 80px}.lede{max-width:640px;margin:8px 0 0}.note{font-size:13px;color:var(--body)}.cards{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:16px;margin-top:24px}.course-card{display:flex;flex-direction:column;gap:8px;min-height:168px;color:inherit;text-decoration:none;overflow-wrap:anywhere;transition:box-shadow .15s}a.course-card:hover{box-shadow:var(--shadow-card-hover);text-decoration:none}.course-card[aria-disabled=true]{opacity:.7}.course-card h2{margin-top:4px}.course-card p{margin:0;flex:1}.actions{display:flex;flex-wrap:wrap;gap:12px;margin-top:24px}.unit-list{list-style:none;padding:0;margin:24px 0 0;display:grid;gap:12px}.unit-row{display:flex;align-items:center;justify-content:space-between;gap:16px;color:inherit;text-decoration:none;overflow-wrap:anywhere;transition:box-shadow .15s}a.unit-row:hover{box-shadow:var(--shadow-card-hover);text-decoration:none}.unit-row h3{margin-bottom:4px}.unit-row p{margin:0;font-size:14px}.unit-row .badge{flex:none}.unit-layout{display:grid;grid-template-columns:240px minmax(0,1fr) 400px;height:calc(100vh - var(--topbar-h))}.unit-nav{border-right:1px solid var(--hair);padding:24px 16px;overflow:auto;display:flex;flex-direction:column;gap:12px}.unit-nav ol{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:2px}.unit-nav a.item{display:flex;justify-content:space-between;gap:8px;padding:8px 10px;border-radius:var(--r-md);color:var(--body);font-size:14px;text-decoration:none}.unit-nav a.item:hover{background:var(--card)}.unit-nav a.item.active{background:var(--green-soft);color:var(--green-deep);font-weight:500}.viewed{font-size:12px;color:var(--body);white-space:nowrap}.unit-main{overflow:auto;padding:32px 40px 80px}.unit-main>*{max-width:760px}.snapshot{font-size:13px;color:var(--body);padding:8px 12px;border-radius:var(--r-md);background:var(--card);box-shadow:inset 0 0 0 1px var(--hair)}.unit-actions{display:flex;flex-wrap:wrap;gap:12px;align-items:center;margin-top:40px;padding-top:24px;border-top:1px solid var(--hair)}.chat-col{border-left:1px solid var(--hair);min-height:0;display:flex;background:var(--page)}.chat-fab{display:none;position:fixed;right:16px;bottom:16px;z-index:40}.prose{font-size:15px;overflow-wrap:anywhere}.prose h1{font-size:20px;margin:8px 0 16px}.prose h2{font-size:16px;margin:32px 0 8px}.prose h3{font-size:15px;margin:24px 0 8px}.prose img{max-width:100%;height:auto}.prose p{margin:8px 0}.prose ul,.prose ol{padding-left:22px;margin:8px 0}.prose li{margin:4px 0}.prose strong{color:var(--ink);font-weight:600}.prose code{font-family:var(--mono);font-size:13px;padding:1px 5px;border-radius:var(--r-sm);background:var(--card);box-shadow:inset 0 0 0 1px var(--hair)}.prose table{display:block;max-width:100%;overflow-x:auto;border-collapse:collapse;font-size:14px}.prose pre{max-width:100%;overflow-x:auto;margin:12px 0;padding:12px 14px;border-radius:var(--r-md);background:var(--card);box-shadow:var(--shadow-card)}.prose pre code{padding:0;background:none;box-shadow:none}.prose th,.prose td{text-align:left;padding:8px 10px;border-bottom:1px solid var(--hair)}.prose blockquote{margin:12px 0;padding:4px 14px;border-left:2px solid var(--hair);color:var(--body)}.tag{display:inline-block;margin-right:6px;padding:0 8px;border:1px solid transparent;border-radius:var(--r-sm);font-size:12px;font-weight:600;line-height:20px;vertical-align:2px;color:var(--ink);background:var(--page)}.tag-ready{color:#fff;background:var(--ink);border-color:var(--ink)}.tag-assist{border:1px solid var(--ink)}.tag-dependency{border:1px dashed var(--ink);background:var(--card)}.tag-planned{font-weight:500;color:var(--body);border:1px dotted var(--muted)}.chat{display:flex;flex-direction:column;min-height:0;width:100%;background:var(--page)}.chat-full{max-width:820px;margin:0 auto;height:calc(100vh - var(--topbar-h) - 220px);min-height:420px;border-radius:var(--r-lg);box-shadow:var(--shadow-card);overflow:hidden}.chat-head{display:flex;justify-content:space-between;align-items:center;padding:14px 16px;border-bottom:1px solid var(--hair)}.chat-head h3{font-size:15px}.chat-notice{padding:12px 16px;background:var(--card);border-bottom:1px solid var(--hair);font-size:13px;color:var(--ink)}.chat-log{flex:1;overflow:auto;padding:16px;display:flex;flex-direction:column;gap:12px}.chat-empty{color:var(--body);font-size:14px}.chips{display:flex;flex-direction:column;gap:8px;margin-top:12px;align-items:flex-start}.chip{padding:6px 12px;border:0;border-radius:var(--r-md);background:var(--page);color:var(--ink);font:400 13px var(--font);text-align:left;cursor:pointer;box-shadow:inset 0 0 0 1px var(--hair)}.chip:hover{background:var(--card);box-shadow:var(--ring-hover)}.chip:disabled{opacity:.45;cursor:not-allowed}.msg{max-width:92%;padding:10px 12px;border-radius:var(--r-lg);font-size:14px;overflow-wrap:anywhere}.msg-user{align-self:flex-end;background:var(--ink);color:#fff;white-space:pre-wrap}.msg-ai{align-self:flex-start;background:var(--card);box-shadow:var(--shadow-card)}.msg-ai .prose{font-size:14px}.msg-ai .prose>:first-child{margin-top:0}.msg-ai .prose>:last-child{margin-bottom:0}.chat-error{padding:8px 16px;font-size:13px;color:var(--ink);background:var(--card);border-top:1px solid var(--hair)}.chat-form{border-top:1px solid var(--hair);padding:12px 16px;display:flex;flex-direction:column;gap:8px}.chat-form textarea{resize:none;min-height:64px;padding:10px 12px;border:0;border-radius:var(--r-md);font:400 14px var(--font);color:var(--ink);background:var(--page);box-shadow:inset 0 0 0 1px var(--hair)}.chat-form textarea:focus-visible{outline:2px solid var(--ink);outline-offset:0}.chat-form textarea:disabled{background:var(--card);color:var(--muted)}.chat-row{display:flex;justify-content:space-between;align-items:center;gap:12px}.chat-row .btn{flex:none}.chat-locked .chat-log{opacity:.45}.quiz-layout{display:grid;grid-template-columns:minmax(0,1fr) 400px;min-height:calc(100vh - var(--topbar-h))}.quiz-main{padding:32px 40px 80px;min-width:0}.quiz-main>*{max-width:760px}.q{min-width:0;margin:24px 0 0;padding:20px;border:0;border-radius:var(--r-lg);background:var(--card);box-shadow:var(--shadow-card)}.q legend{float:left;width:100%;padding:0;margin:0 0 12px;font-weight:600;color:var(--ink)}.q-kind{display:block;margin-bottom:4px;font-size:12px;font-weight:500;letter-spacing:.3px;color:var(--body)}.opt{display:flex;gap:10px;align-items:flex-start;clear:both;padding:10px 12px;margin-top:8px;border-radius:var(--r-md);background:var(--page);box-shadow:inset 0 0 0 1px var(--hair);cursor:pointer}.opt:hover{box-shadow:var(--ring-hover)}.opt span{min-width:0;overflow-wrap:anywhere}.opt input{flex:none;margin-top:5px;accent-color:var(--ink)}.opt.opt-picked{box-shadow:inset 0 0 0 2px var(--ink)}.opt.opt-right{background:var(--green-soft);box-shadow:inset 0 0 0 1px var(--green-deep)}.verdict{margin-top:12px;font-size:14px}.verdict strong{color:var(--ink)}.score-card{margin-top:24px}.score{font-size:36px;font-weight:600;color:var(--ink);letter-spacing:-.6px}@media(max-width:1180px){.unit-layout{grid-template-columns:200px minmax(0,1fr)}.chat-col{position:fixed;right:0;top:var(--topbar-h);bottom:0;width:min(420px,100vw);z-index:30;transform:translate(100%);visibility:hidden;transition:transform .2s,visibility 0s linear .2s;box-shadow:-1px 0 0 var(--hair)}.chat-open .chat-col{transform:none;visibility:visible;transition:transform .2s}.chat-open .chat-form{padding-bottom:72px}.chat-fab{display:inline-flex}.quiz-layout{grid-template-columns:minmax(0,1fr)}.quiz-layout .chat-col{position:static;transform:none;visibility:visible;width:auto;border-left:0;border-top:1px solid var(--hair);box-shadow:none;min-height:360px}}@media(max-width:760px){.topbar{padding:0 16px}.container{padding:24px 16px 64px}.unit-layout{grid-template-columns:minmax(0,1fr);height:auto}.unit-nav{border-right:0;border-bottom:1px solid var(--hair)}.unit-main,.quiz-main{padding:24px 16px 96px}.chat-full{height:70vh}}@media(prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important;scroll-behavior:auto!important}}.lang-toggle{display:inline-flex;padding:2px;border-radius:var(--r-md);box-shadow:inset 0 0 0 1px var(--hair);background:var(--card)}.lang-toggle button{font:inherit;font-size:13px;font-weight:500;line-height:1;padding:6px 10px;border:0;border-radius:var(--r-sm);background:transparent;color:var(--body);cursor:pointer}.lang-toggle button[aria-pressed=true]{background:var(--ink);color:#fff}.lang-toggle button:focus-visible{outline:2px solid var(--ink);outline-offset:1px}.answer-line{display:block;margin-top:4px}.course-group{margin-top:32px}.group-title{margin:0}.code{font-family:var(--mono);font-size:12px;color:var(--body)}.prose img{display:block;margin:16px 0;border-radius:var(--r-md);box-shadow:var(--shadow-card);background:var(--card)}