/* AI series — Ran Wei. Extends the look of the site's other tutorial series. */
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
  --navy:#1A2E4A;--blue:#2563EB;--sky:#0EA5E9;--sky-light:#DBEAFE;--sky-pale:#F0F9FF;
  --slate:#475569;--muted:#94A3B8;--border:#E2E8F0;--bg:#FAFBFD;--white:#FFFFFF;
  --green:#15803D;--green-bg:#F0FDF4;--orange:#C2410C;--orange-bg:#FFF7ED;--red:#DC2626;--red-bg:#FEF2F2;
  --purple:#7E22CE;--purple-bg:#FAF5FF;--amber:#B45309;--amber-bg:#FFFBEB;
  --code-bg:#F1F5F9;--code-text:#0F172A;
  --font-display:'Fraunces',Georgia,'Songti SC','Noto Serif SC',serif;
  --font-body:'DM Sans',system-ui,-apple-system,'Segoe UI','PingFang SC','Hiragino Sans GB','Microsoft YaHei','Noto Sans SC',sans-serif;
  --font-mono:'DM Mono','Fira Code',Consolas,'PingFang SC','Microsoft YaHei',monospace;
  --sidebar-w:270px;--content-max:860px;--radius:10px;--transition:0.2s cubic-bezier(0.4,0,0.2,1)
}
html{scroll-behavior:smooth;font-size:16px}
body{font-family:var(--font-body);background:var(--bg);color:var(--navy);line-height:1.7;min-height:100vh}
html[lang^="zh"] body{line-height:1.85}
a{color:var(--blue)}
#progress-bar{position:fixed;top:0;left:0;height:3px;background:linear-gradient(90deg,var(--sky),var(--blue));width:0%;z-index:1000;transition:width 0.1s linear;box-shadow:0 0 8px rgba(14,165,233,.5)}

/* ---------- top bar ---------- */
#topbar{position:sticky;top:0;z-index:100;background:rgba(250,251,253,.92);backdrop-filter:blur(12px);border-bottom:1px solid var(--border);display:flex;align-items:center;gap:1rem;padding:0 2rem;height:56px}
#topbar .brand{font-family:var(--font-display);font-weight:600;font-size:1.05rem;color:var(--navy);letter-spacing:-.01em;text-decoration:none;white-space:nowrap}
#topbar .brand span{color:var(--sky)}
#topbar .sep{color:var(--border);font-size:1.2rem}
#topbar .crumb{color:var(--slate);font-size:.85rem;font-weight:500;text-decoration:none;white-space:nowrap}
#topbar a.crumb:hover{color:var(--blue)}
.module-dropdown{margin-left:auto;position:relative}
.module-dropdown .badge{background:var(--sky-light);color:var(--blue);font-size:.75rem;font-weight:600;padding:.2rem .65rem .2rem .8rem;border-radius:999px;white-space:nowrap;cursor:pointer;display:flex;align-items:center;gap:.3rem;border:none;font-family:inherit}
.module-dropdown .badge::after{content:'\25BE';font-size:.7rem}
.module-dropdown .dropdown-menu{display:none;position:absolute;top:calc(100% + 6px);right:0;background:var(--white);border:1px solid var(--border);border-radius:10px;box-shadow:0 8px 24px rgba(0,0,0,.1);min-width:300px;padding:.4rem;z-index:200;max-height:70vh;overflow-y:auto}
.module-dropdown.open .dropdown-menu{display:block}
.module-dropdown .dropdown-menu a{display:block;padding:.5rem .75rem;border-radius:7px;font-size:.82rem;font-weight:500;color:var(--slate);text-decoration:none}
.module-dropdown .dropdown-menu a:hover{background:var(--sky-pale);color:var(--blue)}
.module-dropdown .dropdown-menu a.active{background:var(--sky-light);color:var(--blue);font-weight:600}
.lang-switch{font-size:.78rem;font-weight:500;color:var(--slate);text-decoration:none;border:1px solid var(--border);padding:.2rem .6rem;border-radius:6px;margin-left:.5rem;white-space:nowrap}
.lang-switch:hover{border-color:var(--blue);color:var(--blue)}

/* ---------- layout and sidebar ---------- */
#layout{display:flex;min-height:calc(100vh - 56px)}
#sidebar{width:var(--sidebar-w);flex-shrink:0;position:sticky;top:56px;height:calc(100vh - 56px);overflow-y:auto;padding:1.5rem 1rem 2rem 1.25rem;border-right:1px solid var(--border);background:var(--white);scrollbar-width:thin;scrollbar-color:var(--border) transparent}
.sidebar-label{font-size:.7rem;font-weight:600;letter-spacing:.1em;text-transform:uppercase;color:var(--muted);margin:1.25rem 0 .5rem}
.side-group{font-size:.66rem;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:var(--sky);margin:1rem 0 .3rem .75rem}
#sidebar nav{display:flex;flex-direction:column;gap:1px}
#sidebar nav a{display:flex;align-items:flex-start;gap:.6rem;font-size:.82rem;font-weight:500;color:var(--slate);text-decoration:none;padding:.38rem .6rem;border-radius:8px;transition:var(--transition);line-height:1.4}
#sidebar nav a .num{width:20px;height:20px;border-radius:50%;background:var(--border);color:var(--slate);font-size:.66rem;font-weight:700;display:flex;align-items:center;justify-content:center;flex-shrink:0;transition:var(--transition);margin-top:1px}
#sidebar nav a:hover{background:var(--sky-pale);color:var(--blue)}
#sidebar nav a:hover .num{background:var(--sky-light);color:var(--blue)}
#sidebar nav a.active{background:var(--sky-light);color:var(--blue)}
#sidebar nav a.active .num{background:var(--blue);color:#fff}
.side-progress{background:var(--sky-pale);border:1px solid var(--sky-light);border-radius:10px;padding:.65rem .8rem}
.side-progress-label{font-size:.75rem;color:var(--slate);font-weight:500;margin-bottom:.4rem}
.side-progress-bar{height:6px;border-radius:3px;background:var(--white);overflow:hidden;border:1px solid var(--sky-light)}
.side-progress-bar span{display:block;height:100%;width:0;background:linear-gradient(90deg,var(--sky),var(--blue));transition:width .3s}

/* ---------- main column ---------- */
#main{flex:1;padding:3rem 3rem 5rem;min-width:0;max-width:calc(var(--content-max) + 6rem)}
.module-hero{margin-bottom:2.5rem;padding-bottom:2.5rem;border-bottom:1px solid var(--border)}
.module-hero .series{font-size:.8rem;font-weight:600;letter-spacing:.08em;text-transform:uppercase;color:var(--sky);margin-bottom:1rem;display:flex;align-items:center;gap:.5rem}
.module-hero .series::before{content:'';display:block;width:24px;height:2px;background:var(--sky)}
.module-title{font-family:var(--font-display);font-size:clamp(2.1rem,5vw,3.1rem);font-weight:700;color:var(--navy);line-height:1.15;margin-bottom:1rem;letter-spacing:-.03em}
.module-title em{color:var(--blue);font-style:normal}
.module-lead{font-size:1.1rem;color:var(--slate);font-weight:300;max-width:640px;margin-bottom:1.25rem;line-height:1.65}
.hero-chips,.lab-meta{display:flex;flex-wrap:wrap;gap:.45rem}
.chip{font-family:var(--font-mono);font-size:.72rem;font-weight:500;padding:.18rem .65rem;border-radius:999px;background:var(--white);color:var(--slate);border:1px solid var(--border);white-space:nowrap}
.chip-time{background:var(--navy);color:#fff;border-color:var(--navy)}

/* at a glance */
.glance{display:grid;grid-template-columns:3fr 2fr;gap:1.5rem;background:var(--white);border:1px solid var(--border);border-radius:14px;padding:1.5rem 1.75rem;margin-bottom:2rem}
.glance-h{font-family:var(--font-body);font-size:.72rem!important;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--sky)!important;margin:0 0 .6rem!important;display:block!important}
.glance-h::before{display:none!important}
.glance-col ul{margin:0 0 1rem 1.1rem}
.glance-col li{font-size:.9rem;margin-bottom:.3rem}
.glance ul.outcomes{list-style:none;margin-left:0}
.glance ul.outcomes li{position:relative;padding-left:1.5rem}
.glance ul.outcomes li::before{content:'';position:absolute;left:0;top:.45em;width:.9rem;height:.9rem;border-radius:4px;border:2px solid var(--sky)}

/* study plan */
.plan{margin-bottom:3rem}
.plan-head{display:flex;align-items:baseline;gap:1rem;flex-wrap:wrap}
.plan-title{font-family:var(--font-display);font-size:1.6rem;font-weight:600;letter-spacing:-.02em}
.plan-total{font-family:var(--font-mono);font-size:.8rem;color:var(--slate)}
.plan-lead{font-size:.9rem!important;margin:.35rem 0 1.1rem!important}
.sessions{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:.9rem}
.session{background:var(--white);border:1px solid var(--border);border-radius:12px;padding:1rem 1.1rem;display:flex;flex-direction:column;transition:var(--transition)}
.session.is-done{border-color:var(--green);background:var(--green-bg)}
.session-head{display:flex;justify-content:space-between;align-items:center;margin-bottom:.25rem}
.session-n{font-family:var(--font-mono);font-size:.72rem;font-weight:500;color:var(--white);background:var(--navy);padding:.1rem .55rem;border-radius:999px}
.session-min{font-family:var(--font-mono);font-size:.72rem;color:var(--muted)}
.session-title{font-family:var(--font-display);font-weight:600;font-size:1rem;line-height:1.3;margin:.35rem 0 .6rem}
.acts{list-style:none;margin:0 0 .75rem!important;flex:1}
.act{display:grid;grid-template-columns:auto 1fr auto;gap:.5rem;align-items:baseline;font-size:.8rem;padding:.25rem 0;border-top:1px dashed var(--border);margin:0!important}
.act-kind{font-family:var(--font-mono);font-size:.62rem;text-transform:uppercase;letter-spacing:.06em;padding:.05rem .4rem;border-radius:4px;background:var(--sky-pale);color:var(--blue)}
.act-lab .act-kind{background:var(--green-bg);color:var(--green)}
.act-exercises .act-kind,.act-quiz .act-kind{background:var(--orange-bg);color:var(--orange)}
.act-papers .act-kind{background:var(--purple-bg);color:var(--purple)}
.act-review .act-kind{background:var(--amber-bg);color:var(--amber)}
.act-what a{color:var(--navy);text-decoration:none}
.act-what a:hover{color:var(--blue);text-decoration:underline}
.act-min{font-family:var(--font-mono);font-size:.7rem;color:var(--muted)}
.session-done{font-size:.8rem;color:var(--slate);display:flex;align-items:center;gap:.4rem;cursor:pointer;user-select:none}
.session-done input{accent-color:var(--green);width:15px;height:15px}

/* ---------- section structure ---------- */
.section-anchor{display:block;height:80px;margin-top:-80px;visibility:hidden}
.section-header{display:flex;align-items:center;gap:1rem;margin:3.5rem 0 .4rem;padding-bottom:1rem;border-bottom:2px solid var(--sky-light)}
.section-header .section-num{min-width:36px;height:36px;padding:0 .4rem;border-radius:10px;background:var(--navy);color:#fff;font-family:var(--font-display);font-size:1rem;font-weight:700;display:flex;align-items:center;justify-content:center;flex-shrink:0}
.section-header h2{font-family:var(--font-display);font-size:1.6rem;font-weight:600;color:var(--navy);letter-spacing:-.02em;line-height:1.25}
.section-header[data-sec^="lab"] .section-num{background:var(--green)}
.section-header[data-sec^="lab"]{border-bottom-color:#BBF7D0}
.sec-meta{font-family:var(--font-mono);font-size:.72rem;color:var(--muted);margin:0 0 1.5rem}
.lab-meta{margin:0 0 1.5rem}
.content h3{font-size:1.08rem;font-weight:600;color:var(--blue);margin:2.2rem 0 .75rem;display:flex;align-items:center;gap:.5rem;line-height:1.35}
.content h3::before{content:'';display:block;width:3px;height:1em;background:var(--sky);border-radius:2px;flex-shrink:0}
.content h4{font-size:.98rem;font-weight:600;color:var(--navy);margin:1.6rem 0 .5rem}
.content p{margin-bottom:1rem;color:var(--slate);font-size:.98rem}
.content p strong,.content li strong{color:var(--navy)}
.content ul,.content ol{margin:.5rem 0 1rem 1.5rem}
.content li{margin-bottom:.35rem;color:var(--slate);font-size:.98rem}
.content li>p{margin-bottom:.4rem}
.content blockquote{border-left:3px solid var(--border);padding:.2rem 0 .2rem 1rem;margin:1rem 0;color:var(--slate)}
.content hr{border:none;border-top:1px solid var(--border);margin:2rem 0}
p,li{color:var(--slate)}

/* ---------- code ---------- */
code{font-family:var(--font-mono);font-size:.86em;background:var(--code-bg);padding:.1em .35em;border-radius:4px;color:var(--code-text)}
pre{position:relative;background:var(--code-bg);border-radius:10px;padding:1.1rem 1.4rem;overflow-x:auto;margin:1.25rem 0;border:1px solid var(--border);font-family:var(--font-mono);font-size:.8rem;line-height:1.65;color:var(--code-text)}
pre code{background:none;padding:0;font-size:inherit;line-height:inherit;color:inherit;border-radius:0}
.copy-btn{position:absolute;top:.5rem;right:.5rem;font-family:var(--font-body);font-size:.7rem;font-weight:600;padding:.15rem .55rem;border-radius:6px;border:1px solid var(--border);background:var(--white);color:var(--slate);cursor:pointer;opacity:0;transition:var(--transition)}
pre:hover .copy-btn,.copy-btn:focus{opacity:1}
.copy-btn.ok{color:var(--green);border-color:var(--green)}
.output{margin:-.6rem 0 1.4rem;border:1px solid var(--border);border-radius:0 0 10px 10px;background:#0F172A}
.output-label{font-family:var(--font-mono);font-size:.62rem;letter-spacing:.12em;text-transform:uppercase;color:#7DD3FC;padding:.45rem 1rem 0}
.output pre{background:none;border:none;margin:0;color:#E2E8F0;padding:.4rem 1rem .9rem;font-size:.78rem}
pre+.output{border-top:none}
/* highlight.js, light */
.hljs-comment,.hljs-quote{color:#64748B;font-style:italic}
.hljs-keyword,.hljs-selector-tag,.hljs-meta .hljs-keyword{color:#7C3AED}
.hljs-built_in,.hljs-type{color:#0369A1}
.hljs-string,.hljs-regexp,.hljs-meta .hljs-string{color:#15803D}
.hljs-number,.hljs-literal{color:#C2410C}
.hljs-title,.hljs-title.function_,.hljs-title.class_{color:#1D4ED8;font-weight:500}
.hljs-params{color:#0F172A}
.hljs-attr,.hljs-attribute,.hljs-variable,.hljs-template-variable{color:#B45309}
.hljs-meta{color:#0E7490}
.hljs-subst{color:#0F172A}

/* ---------- math ---------- */
.katex{font-size:1.06em}
.math-d{display:block;overflow-x:auto;overflow-y:hidden;padding:.35rem 0;margin:.9rem 0 1.1rem;text-align:center}
.math-d .katex-display{margin:0}
span.math-d{margin:.6rem 0}
.math-err{color:var(--red);font-family:var(--font-mono);font-size:.8rem}

/* ---------- callouts and boxes ---------- */
.callout{border-radius:10px;padding:1rem 1.25rem;margin:1.5rem 0;font-size:.93rem;border-left:4px solid}
.callout p,.callout li{font-size:.93rem!important}
.callout p:last-child{margin-bottom:0}
.callout-label{font-size:.72rem;font-weight:700;letter-spacing:.1em;text-transform:uppercase;margin-bottom:.35rem}
.callout.note{background:var(--sky-pale);border-color:var(--blue)}.callout.note .callout-label{color:var(--blue)}
.callout.tip{background:var(--green-bg);border-color:var(--green)}.callout.tip .callout-label{color:var(--green)}
.callout.analogy{background:var(--orange-bg);border-color:var(--orange)}.callout.analogy .callout-label{color:var(--orange)}
.callout.pitfall{background:var(--red-bg);border-color:var(--red)}.callout.pitfall .callout-label{color:var(--red)}
.callout.keyidea{background:var(--navy);border-color:var(--sky);color:#E2E8F0}
.callout.keyidea .callout-label{color:#7DD3FC}
.callout.keyidea p,.callout.keyidea li{color:#E2E8F0!important}
.callout.keyidea strong{color:#fff!important}
.callout.keyidea code{background:rgba(255,255,255,.12);color:#fff}
.worked{background:var(--purple-bg);border:1px solid #E9D5FF;border-radius:12px;padding:1.1rem 1.4rem;margin:1.75rem 0}
.worked-label{font-size:.7rem;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--purple)}
.worked-title{font-family:var(--font-display);font-weight:600;font-size:1.05rem;color:var(--navy);margin:.2rem 0 .6rem}
.worked p:last-child{margin-bottom:0}
.check{background:var(--white);border:1px solid var(--sky-light);border-left:4px solid var(--sky);border-radius:10px;padding:.9rem 1.2rem .6rem;margin:1.5rem 0 .2rem}
.check-label{font-size:.7rem;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--sky);margin-bottom:.35rem}
.check+details.answer{margin:0 0 1.5rem;border-top:none;border-radius:0 0 10px 10px;border-left:4px solid var(--sky)}
details{border:1px solid var(--border);border-radius:10px;background:var(--white);margin:.75rem 0 1.25rem}
details>summary{cursor:pointer;font-size:.82rem;font-weight:600;color:var(--blue);padding:.55rem 1rem;list-style:none;display:flex;align-items:center;gap:.45rem;user-select:none}
details>summary::-webkit-details-marker{display:none}
details>summary::before{content:'\25B8';transition:transform .15s}
details[open]>summary::before{transform:rotate(90deg)}
.details-body{padding:.2rem 1.2rem 1rem;border-top:1px dashed var(--border)}
.details-body p:last-child{margin-bottom:0}

/* exercises */
.exercise{background:var(--white);border:1px solid var(--border);border-radius:12px 12px 0 0;padding:1rem 1.25rem .4rem;margin:1.5rem 0 0}
.exercise-head{display:flex;flex-wrap:wrap;align-items:center;gap:.6rem;margin-bottom:.5rem}
.exercise-n{font-family:var(--font-display);font-weight:700;color:var(--navy);font-size:1.02rem}
.stars{color:#F59E0B;letter-spacing:.05em;font-size:.9rem}
.stars-off{color:var(--border)}
.exercise-kind,.exercise-time{font-family:var(--font-mono);font-size:.68rem;padding:.08rem .5rem;border-radius:999px;background:var(--code-bg);color:var(--slate)}
.exercise+details.solution{margin-top:0;border-top:none;border-radius:0 0 12px 12px}
.exercise:not(:has(+ details.solution)){border-radius:12px;padding-bottom:.6rem;margin-bottom:1rem}

/* papers */
.paper{background:var(--white);border:1px solid var(--border);border-top:4px solid var(--purple);border-radius:12px;padding:1.1rem 1.4rem;margin:1.5rem 0}
.paper-label{font-size:.7rem;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--purple);margin-bottom:.4rem}
.paper p:first-of-type{color:var(--navy);font-weight:500}

/* figures */
figure.fig{margin:2rem 0;background:var(--white);border:1px solid var(--border);border-radius:12px;padding:1.25rem 1.25rem .9rem}
.fig-svg{display:flex;justify-content:center;overflow-x:auto}
.fig-svg svg{max-width:100%;height:auto}
figure.fig figcaption{font-size:.85rem;color:var(--slate);margin-top:.8rem;line-height:1.55}
figure.fig figcaption p{display:inline;font-size:.85rem}
.fig-num{font-weight:700;color:var(--navy);margin-right:.3rem}
.fig-missing{font-family:var(--font-mono);font-size:.8rem;color:var(--red);padding:2rem;text-align:center;border:2px dashed var(--red-bg);width:100%}
figure.lab-plot{margin:-.6rem 0 1.4rem;border:1px solid var(--border);border-top:none;border-radius:0 0 10px 10px;background:var(--white);padding:.75rem;text-align:center}
figure.lab-plot img{max-width:100%;height:auto}
figure.lab-plot figcaption{font-size:.75rem;color:var(--muted);font-family:var(--font-mono)}

/* tables */
.table-wrap{overflow-x:auto;margin:1.5rem 0;border-radius:10px;border:1px solid var(--border)}
table{width:100%;border-collapse:collapse;font-size:.88rem}
th{background:var(--navy);color:#fff;font-weight:600;text-align:left;padding:.6rem 1rem;font-size:.82rem}
td{padding:.55rem 1rem;color:var(--slate);vertical-align:top;border-bottom:1px solid var(--border)}
td:first-child{color:var(--navy);font-weight:500}
tbody tr:last-child td{border-bottom:none}
tbody tr:hover{background:var(--sky-pale)}

/* ---------- quiz ---------- */
.quiz{margin:1.5rem 0}
.quiz-q{background:var(--white);border:1px solid var(--border);border-radius:12px;padding:1rem 1.25rem;margin-bottom:1rem}
.quiz-stem{display:flex;gap:.75rem;align-items:flex-start;color:var(--navy);font-weight:500;font-size:.95rem}
.quiz-stem p{color:var(--navy)}
.quiz-n{font-family:var(--font-mono);font-size:.75rem;background:var(--navy);color:#fff;border-radius:6px;padding:.05rem .45rem;margin-top:.15rem;flex-shrink:0}
.quiz-opts{list-style:upper-alpha;margin:.75rem 0 0 2.6rem!important}
.quiz-opts li{margin-bottom:.4rem;padding-left:.2rem}
.quiz-opt{width:100%;text-align:left;font:inherit;font-size:.9rem;color:var(--slate);background:var(--bg);border:1px solid var(--border);border-radius:8px;padding:.45rem .8rem;cursor:pointer;transition:var(--transition)}
.quiz-opt:hover:not(:disabled){border-color:var(--blue);color:var(--navy)}
.quiz-opt:disabled{cursor:default}
.quiz-opt.right{background:var(--green-bg);border-color:var(--green);color:var(--green);font-weight:500}
.quiz-opt.wrong{background:var(--red-bg);border-color:var(--red);color:var(--red)}
.quiz-expl{margin:.6rem 0 0 2.6rem;font-size:.88rem;color:var(--slate);background:var(--sky-pale);border-radius:8px;padding:.6rem .9rem}
.quiz-bar{display:flex;align-items:center;gap:1rem;justify-content:flex-end}
.quiz-score{font-family:var(--font-mono);font-size:.85rem;color:var(--navy)}
.quiz-reset{font:inherit;font-size:.8rem;font-weight:600;color:var(--blue);background:var(--white);border:1px solid var(--border);border-radius:8px;padding:.35rem .9rem;cursor:pointer}

/* ---------- interactive widgets ---------- */
.widget-wrap{margin:2rem 0;border:1px solid var(--sky-light);border-radius:14px;background:var(--white);overflow:hidden;box-shadow:0 2px 12px rgba(37,99,235,.05)}
.widget-label{font-size:.68rem;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:var(--white);background:linear-gradient(90deg,var(--blue),var(--sky));padding:.35rem 1rem}
.widget{padding:1rem 1.25rem;min-height:120px}
.widget-caption{padding:0 1.25rem .9rem;font-size:.85rem;color:var(--slate)}
.widget-caption p{font-size:.85rem;margin-bottom:.4rem}
.widget-caption:empty{display:none}
.w-row{display:flex;flex-wrap:wrap;gap:1rem;align-items:flex-start}
.w-col{flex:1 1 260px;min-width:0}
.w-controls{display:flex;flex-wrap:wrap;gap:.6rem 1.25rem;margin-bottom:.9rem}
.w-ctl{display:flex;flex-direction:column;gap:.2rem;min-width:150px;font-size:.78rem;color:var(--slate)}
.w-ctl>span:first-child{font-weight:600;color:var(--navy)}
.w-val{font-family:var(--font-mono);font-size:.75rem;color:var(--blue)}
.widget input[type=range]{width:100%;accent-color:var(--blue)}
.widget select,.widget input[type=number],.widget input[type=text]{font:inherit;font-size:.82rem;padding:.3rem .5rem;border:1px solid var(--border);border-radius:6px;background:var(--white);color:var(--navy)}
.widget input[type=number]{width:4.5rem;font-family:var(--font-mono)}
.w-btn{font:inherit;font-size:.8rem;font-weight:600;padding:.35rem .9rem;border-radius:8px;border:1px solid var(--blue);background:var(--blue);color:#fff;cursor:pointer}
.w-btn.secondary{background:var(--white);color:var(--blue)}
.w-btn:disabled{opacity:.5;cursor:default}
.w-canvas{display:block;width:100%;border:1px solid var(--border);border-radius:8px;background:#fff;touch-action:none}
.w-readout{font-family:var(--font-mono);font-size:.78rem;color:var(--navy);background:var(--code-bg);border-radius:8px;padding:.5rem .75rem;line-height:1.6;white-space:pre-wrap}
.w-note{font-size:.8rem;color:var(--muted);margin-top:.4rem}
.w-legend{display:flex;flex-wrap:wrap;gap:.8rem;font-size:.75rem;color:var(--slate);margin:.4rem 0}
.w-legend i{display:inline-block;width:12px;height:3px;border-radius:2px;margin-right:.3rem;vertical-align:middle}
.w-matrix{display:inline-grid;gap:3px;padding:4px 6px;border-left:2px solid var(--navy);border-right:2px solid var(--navy);border-radius:4px}
.w-matrix input{width:3.4rem;text-align:center}
.w-table{border-collapse:collapse;font-family:var(--font-mono);font-size:.75rem}
.w-table td,.w-table th{padding:.2rem .45rem;border:1px solid var(--border);text-align:right;background:none;color:var(--navy);font-weight:400}

/* ---------- module navigation and footer ---------- */
.module-nav{display:grid;grid-template-columns:1fr 1fr;gap:1rem;margin:4rem 0 0}
.mnav{display:block;text-decoration:none;border:1px solid var(--border);border-radius:12px;padding:1rem 1.25rem;background:var(--white);transition:var(--transition)}
.mnav:hover{border-color:var(--blue);transform:translateY(-2px);box-shadow:0 6px 20px rgba(0,0,0,.06)}
.mnav.next{text-align:right;background:var(--sky-pale);border-color:var(--sky-light)}
.mnav-label{display:block;font-size:.7rem;font-weight:700;letter-spacing:.08em;text-transform:uppercase;color:var(--sky);margin-bottom:.2rem}
.mnav-title{display:block;font-weight:600;color:var(--navy);font-size:.95rem}
.site-footer{margin-top:3rem;padding:1.5rem;text-align:center;font-size:.85rem;color:var(--muted);border-top:1px solid var(--border)}
.site-footer a{color:#38bdf8;text-decoration:none}

/* ---------- index page ---------- */
.site-nav{position:sticky;top:0;z-index:100;background:rgba(250,251,253,.92);backdrop-filter:blur(12px);border-bottom:1px solid var(--border);padding:0 2rem;height:56px;display:flex;align-items:center;gap:.6rem}
.nav-brand{font-family:var(--font-display);font-weight:600;font-size:1.05rem;color:var(--navy);text-decoration:none;letter-spacing:-.01em}
.nav-brand span{color:var(--sky)}
.nav-sep{color:var(--border);font-size:1.2rem}
.nav-crumb{font-size:.85rem;font-weight:500;color:var(--slate);text-decoration:none}
.site-nav .lang-switch{margin-left:auto}
.index-hero{padding:5rem 2rem 3rem;max-width:1100px;margin:0 auto;border-bottom:1px solid var(--border)}
.index-hero h1{font-family:var(--font-display);font-size:clamp(2.2rem,5vw,3.8rem);font-weight:700;line-height:1.12;letter-spacing:-.03em;margin-bottom:1.25rem}
.index-hero h1 em{color:var(--blue);font-style:normal}
.index-hero .lead{font-size:1.15rem;color:var(--slate);max-width:640px;line-height:1.65;margin-bottom:1.5rem;font-weight:300}
.hero-tags{display:flex;gap:1rem;flex-wrap:wrap;margin-top:1rem}
.tag{font-family:var(--font-mono);font-size:11px;font-weight:500;padding:3px 10px;border-radius:20px;letter-spacing:.04em;white-space:nowrap}
.tag-module{background:var(--navy);color:#fff}.tag-theme{background:var(--sky-light);color:var(--blue)}.tag-time{background:var(--bg);color:var(--muted);border:1px solid var(--border)}
.index-body{max-width:1100px;margin:0 auto;padding:2.5rem 2rem 0}
.index-body .content-cols{display:grid;grid-template-columns:repeat(auto-fit,minmax(300px,1fr));gap:1.25rem}
.index-body h2{font-family:var(--font-display);font-size:1.6rem;font-weight:600;letter-spacing:-.02em;margin:2rem 0 1rem}
.index-body h3{font-size:1.02rem;font-weight:600;color:var(--blue);margin:1.5rem 0 .5rem}
.index-body p,.index-body li{font-size:.97rem;color:var(--slate);margin-bottom:.75rem}
.index-body ul,.index-body ol{margin:.5rem 0 1rem 1.5rem}
.index-body .section-anchor{height:70px;margin-top:-70px}
.index-body .section-header{margin-top:2.5rem}
.index-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(310px,1fr));gap:1.25rem;padding:2rem 2rem;max-width:1100px;margin:0 auto}
.index-note{max-width:1100px;margin:-.75rem auto 0;padding:0 2rem;color:var(--slate);font-size:.95rem}
.module-card{background:var(--white);border:1px solid var(--border);border-radius:var(--radius);padding:1.5rem;text-decoration:none;transition:all .2s;display:flex;flex-direction:column}
.module-card:hover{transform:translateY(-2px);box-shadow:0 8px 28px rgba(0,0,0,.08);border-color:var(--blue)}
.card-num{font-family:var(--font-mono);font-size:11px;color:var(--muted);margin-bottom:8px}
.card-title{font-family:var(--font-display);font-size:1.08rem;font-weight:700;color:var(--navy);margin-bottom:8px;line-height:1.3}
.card-desc{font-size:13px;color:var(--slate);line-height:1.55;flex:1}
.card-meta{font-family:var(--font-mono);font-size:11px;color:var(--blue);margin-top:.75rem}
.card-footer{display:flex;align-items:center;justify-content:space-between;margin-top:.8rem}
.card-theme{font-family:var(--font-mono);font-size:11px;padding:2px 8px;border-radius:20px}
.card-lang{font-family:var(--font-mono);font-size:11px;color:var(--muted)}
.theme-foundations{background:#E2E8F0;color:#475569}.theme-architectures{background:#DBEAFE;color:#2563EB}.theme-llm{background:#EDE9FE;color:#7C3AED}

/* ---------- responsive and print ---------- */
@media(max-width:1100px){.glance{grid-template-columns:1fr}}
@media(max-width:900px){#sidebar{display:none}#main{padding:2rem 1.25rem 4rem}#topbar{padding:0 1rem;gap:.6rem}#topbar .crumb-now{display:none}.module-nav{grid-template-columns:1fr}}
@media(max-width:600px){.index-hero{padding:3rem 1.25rem 2rem}.index-grid{padding:1.5rem 1.25rem}.index-note{padding:0 1.25rem}.index-body{padding:1.5rem 1.25rem 0}.index-hero h1{font-size:2rem}#topbar .crumb,#topbar .sep{display:none}pre{padding:1rem}.widget{padding:.9rem}.quiz-opts{margin-left:1.2rem!important}.quiz-expl{margin-left:0}}
@media print{#topbar,#sidebar,#progress-bar,.module-nav,.copy-btn,.session-done{display:none!important}#main{padding:0;max-width:none}details{border:none}details>summary{display:none}details .details-body{display:block}}