:root{
  --paper:#f4f0e8;
  --surface:#fffdf8;
  --ink:#17231d;
  --muted:#4d5a53;
  --accent:#0d6b4f;
  --accent-dark:#0a503c;
  --line:#9baa9f;
  --control-line:#66736a;
  --line-soft:#d2d9d3;
  --soft-green:#e7f1eb;
  --soft-warm:#eee8dc;
  --danger:#983336;
  --danger-bg:#f8e9e7;
  --success:#0d6b4f;
  --focus:#17231d;
  --radius-sm:4px;
  --radius-md:8px;
  --radius-lg:14px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:var(--paper);
  color:var(--ink);
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  line-height:1.58;
}
a{color:inherit}
button,input,textarea,select{font:inherit;color:inherit}
button,a,summary,input,textarea,select{touch-action:manipulation}
code{
  font-family:"SFMono-Regular",Consolas,"Liberation Mono",monospace;
  font-size:.94em;
  overflow-wrap:anywhere;
}
.skip-link{
  position:absolute;
  left:12px;
  top:-80px;
  z-index:100;
  padding:10px 14px;
  background:var(--ink);
  color:#fff;
}
.skip-link:focus{top:12px}
.site-header{
  position:sticky;
  top:0;
  z-index:20;
  background:var(--surface);
  border-bottom:1px solid var(--line);
}
.nav-shell{
  width:min(1160px,calc(100% - 40px));
  min-height:58px;
  margin:auto;
  display:flex;
  align-items:center;
  gap:24px;
}
.brand{
  margin-right:auto;
  text-decoration:none;
  font-family:Georgia,"Times New Roman",serif;
  font-weight:700;
  font-size:1.03rem;
}
.desktop-nav{display:flex;align-items:center;gap:6px}
.desktop-nav a{
  min-height:44px;
  display:flex;
  align-items:center;
  padding:0 10px;
  text-decoration:none;
  color:var(--muted);
  font-size:.9rem;
}
.desktop-nav a:hover{color:var(--accent)}
.mobile-nav{display:none}
.mobile-nav summary{
  min-width:64px;
  min-height:44px;
  display:flex;
  align-items:center;
  justify-content:center;
  cursor:pointer;
  border:1px solid var(--control-line);
  border-radius:var(--radius-sm);
  list-style:none;
  font-weight:700;
}
.mobile-nav summary::-webkit-details-marker{display:none}
.mobile-nav nav{
  position:absolute;
  right:20px;
  top:54px;
  width:min(260px,calc(100vw - 40px));
  background:var(--surface);
  border:1px solid var(--line);
  padding:8px;
  box-shadow:0 12px 24px rgba(23,35,29,.12);
}
.mobile-nav nav a{
  display:flex;
  align-items:center;
  min-height:46px;
  padding:8px 10px;
  text-decoration:none;
  border-bottom:1px solid var(--line-soft);
}
.mobile-nav nav a:last-child{border-bottom:0}

button,
input,
textarea,
select,
a,
summary,
.table-wrap[tabindex]{
  outline:3px solid transparent;
  outline-offset:2px;
}
button:focus-visible,
input:focus-visible,
textarea:focus-visible,
select:focus-visible,
a:focus-visible,
summary:focus-visible,
.table-wrap[tabindex]:focus-visible{
  outline-color:var(--focus);
}

main{
  width:min(1160px,calc(100% - 40px));
  margin:auto;
}
.masthead{
  display:grid;
  grid-template-columns:minmax(0,1.25fr) minmax(320px,.75fr);
  gap:52px;
  align-items:start;
  padding:68px 0 54px;
  border-bottom:3px double var(--line);
}
.course-label{
  margin:0 0 12px;
  color:var(--accent-dark);
  font-weight:800;
  font-size:.9rem;
}
h1,h2,h3,h4,p{margin-top:0}
h1,h2,h3,h4{
  font-family:Georgia,"Times New Roman",serif;
  line-height:1.14;
}
h1{
  max-width:800px;
  margin-bottom:22px;
  font-size:clamp(2.7rem,6vw,5.5rem);
  letter-spacing:-.035em;
}
.lead{
  max-width:760px;
  margin:0;
  color:var(--muted);
  font-size:clamp(1rem,1.5vw,1.18rem);
}
.required-vector{
  border-top:5px solid var(--accent);
  border-bottom:1px solid var(--line);
  padding:18px 0 20px;
}
.vector-heading{
  display:flex;
  align-items:baseline;
  gap:12px;
  margin-bottom:12px;
}
.section-index{
  color:var(--accent-dark);
  font-size:.78rem;
  font-weight:800;
}
.required-vector h2{
  margin:0;
  font-size:1.2rem;
}
.vector-data{margin:0 0 18px}
.vector-data div{
  display:grid;
  grid-template-columns:126px minmax(0,1fr);
  gap:12px;
  padding:9px 0;
  border-bottom:1px solid var(--line-soft);
}
.vector-data dt{color:var(--muted);font-size:.82rem}
.vector-data dd{margin:0;font-weight:700}
.vector-data .expected-row dd{color:var(--accent-dark)}

.lesson-section{
  scroll-margin-top:76px;
  padding:56px 0;
  border-bottom:1px solid var(--line);
}
.section-intro{
  display:grid;
  grid-template-columns:72px minmax(0,760px);
  gap:20px;
  margin-bottom:28px;
}
.section-number{
  font-family:Georgia,"Times New Roman",serif;
  color:var(--accent-dark);
  font-size:2rem;
  line-height:1;
}
.section-intro h2{
  margin-bottom:8px;
  font-size:clamp(1.85rem,3.5vw,2.7rem);
  letter-spacing:-.02em;
}
.section-intro p{margin:0;color:var(--muted)}

.workbench{
  display:grid;
  grid-template-columns:repeat(2,minmax(0,1fr));
  border:1px solid var(--line);
  background:var(--surface);
}
.work-panel{padding:26px}
.work-panel + .work-panel{border-left:1px solid var(--line)}
.panel-heading{margin-bottom:16px}
.panel-kicker{
  display:block;
  margin-bottom:5px;
  color:var(--accent-dark);
  font-size:.78rem;
  font-weight:800;
}
.panel-heading h3,.schedule-input h3,.test-toolbar h3,.keyspace-calculator h3{
  margin:0;
  font-size:1.45rem;
}
label{
  display:block;
  margin:15px 0 6px;
  font-weight:750;
}
input,textarea,select{
  width:100%;
  border:1px solid var(--control-line);
  border-radius:var(--radius-sm);
  background:#fff;
  padding:11px 12px;
}
textarea{
  min-height:108px;
  resize:vertical;
}
input:hover,textarea:hover,select:hover{border-color:var(--accent)}
.two-field-row{
  display:grid;
  grid-template-columns:minmax(0,1.4fr) minmax(145px,.6fr);
  gap:14px;
  align-items:start;
}
.field-help{
  margin:6px 0 0;
  color:var(--muted);
  font-size:.82rem;
}
.btn{
  min-height:44px;
  border:1px solid transparent;
  border-radius:var(--radius-sm);
  padding:9px 14px;
  font-weight:800;
}
.btn.primary{
  margin-top:16px;
  background:var(--accent);
  color:#fff;
  border-color:var(--accent);
}
.btn.primary:hover{background:var(--accent-dark);border-color:var(--accent-dark)}
.text-btn{
  min-height:36px;
  padding:5px 8px;
  background:transparent;
  border-color:var(--control-line);
  color:var(--accent-dark);
}
.text-btn:hover{background:var(--soft-green)}
.error-message{
  margin-top:12px;
  border-left:4px solid var(--danger);
  background:var(--danger-bg);
  padding:10px 12px;
  color:#6f2023;
  font-weight:700;
}
.output-block{
  margin-top:18px;
  padding-top:14px;
  border-top:1px solid var(--line);
}
.output-label{
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:10px;
  margin-bottom:8px;
  color:var(--muted);
  font-size:.82rem;
}
.output-value{
  min-height:54px;
  display:flex;
  align-items:center;
  padding:10px 12px;
  border:1px solid var(--line-soft);
  background:var(--soft-green);
  font-family:"SFMono-Regular",Consolas,"Liberation Mono",monospace;
  font-weight:700;
  overflow-wrap:anywhere;
}
.output-value.is-empty{
  background:var(--soft-warm);
  color:var(--muted);
  font-family:inherit;
  font-weight:500;
}
.output-meta{
  margin-top:6px;
  color:var(--muted);
  font-size:.78rem;
}
.concept-note{
  display:grid;
  grid-template-columns:230px minmax(0,1fr);
  gap:32px;
  margin-top:26px;
  padding:22px 0;
  border-top:1px solid var(--line);
}
.concept-note h3{margin:0;font-size:1.25rem}
.process-list{
  display:grid;
  grid-template-columns:repeat(2,minmax(0,1fr));
  gap:0;
  margin:0;
  padding:0;
  list-style:none;
  border-top:1px solid var(--line-soft);
}
.process-list li{
  padding:14px 16px;
  border-bottom:1px solid var(--line-soft);
}
.process-list li:nth-child(odd){border-right:1px solid var(--line-soft)}
.process-list strong{display:block;margin-bottom:3px}
.process-list span{color:var(--muted);font-size:.88rem}

.schedule-tool,.test-tool{
  background:var(--surface);
  border:1px solid var(--line);
}
.schedule-input,.test-toolbar{padding:22px 24px;border-bottom:1px solid var(--line)}
.schedule-controls{
  display:grid;
  grid-template-columns:minmax(0,1fr) auto;
  gap:14px;
  align-items:end;
  margin-top:12px;
}
.schedule-controls .btn{margin:0}
.schedule-stages{
  max-width:760px;
  margin:28px auto;
  display:grid;
  gap:10px;
}
.schedule-stages article{
  border-left:5px solid var(--accent);
  background:var(--soft-green);
  padding:14px 16px;
}
.schedule-stages article>span,.split-stage span{
  display:block;
  margin-bottom:5px;
  color:var(--muted);
  font-size:.78rem;
}
.schedule-stages code{font-weight:800}
.stage-arrow{
  text-align:center;
  color:var(--accent-dark);
  font-size:1.35rem;
}
.split-stage{
  display:grid;
  grid-template-columns:1fr 1fr;
  gap:1px;
}
.split-stage div + div{border-left:1px solid var(--line)}
.split-stage div{padding:0 10px}
.parity{
  margin:0 24px 20px;
  padding:10px 12px;
  border-left:4px solid var(--line);
  color:var(--muted);
}
.parity.good{border-color:var(--success);background:var(--soft-green);color:var(--ink)}
.parity.info{border-color:#8a6620;background:#f5eedc;color:#5d491f}
.table-wrap{
  width:100%;
  overflow-x:auto;
  border-top:1px solid var(--line);
  border-bottom:1px solid var(--line);
}
table{
  width:100%;
  border-collapse:collapse;
  min-width:860px;
  background:#fff;
}
th,td{
  padding:11px 13px;
  text-align:left;
  vertical-align:top;
  border-bottom:1px solid var(--line-soft);
}
th{
  background:#e9eee9;
  color:var(--ink);
  font-size:.8rem;
}
td{color:var(--muted);font-size:.86rem}
tbody tr:last-child td{border-bottom:0}
td small{display:block;margin-top:4px;color:var(--muted)}
.round-key{color:var(--accent-dark);font-weight:700}
.key-order-block{
  display:grid;
  grid-template-columns:1fr 1fr;
  gap:0;
}
.key-order-block>div{padding:22px 24px}
.key-order-block>div+div{border-left:1px solid var(--line)}
.key-order-block h4{margin-bottom:6px}
.key-order-block p{margin:0;color:var(--muted);font-size:.86rem}
.key-order{
  display:flex;
  align-items:center;
  gap:5px;
  overflow-x:auto;
  margin-top:12px;
  padding-bottom:8px;
}
.key-pill{
  flex:0 0 auto;
  min-width:36px;
  padding:6px 7px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:#fff;
  text-align:center;
  font-family:"SFMono-Regular",Consolas,"Liberation Mono",monospace;
  font-size:.74rem;
  font-weight:800;
}
.key-pill.reverse{background:var(--soft-warm)}
.arrow{color:var(--muted);flex:0 0 auto}

.test-toolbar{
  display:flex;
  align-items:end;
  justify-content:space-between;
  gap:20px;
}
.test-actions{display:flex;align-items:center;gap:12px;flex-wrap:wrap}
.test-actions .btn{margin:0}
.test-summary{font-weight:800}
.pass-summary{color:var(--success)}
.fail-summary{color:var(--danger)}
.status{
  display:inline-block;
  padding:3px 7px;
  border:1px solid currentColor;
  border-radius:var(--radius-sm);
  font-size:.74rem;
  font-weight:900;
}
.status.pass{color:var(--success);background:var(--soft-green)}
.status.fail{color:var(--danger);background:var(--danger-bg)}

.validation-list{
  margin:0;
  border-top:1px solid var(--line);
}
.validation-list div{
  display:grid;
  grid-template-columns:220px minmax(0,1fr);
  gap:24px;
  padding:15px 0;
  border-bottom:1px solid var(--line-soft);
}
.validation-list dt{font-weight:800}
.validation-list dd{margin:0;color:var(--muted)}

.security-layout{
  display:grid;
  grid-template-columns:minmax(0,.85fr) minmax(0,1.15fr);
  border:1px solid var(--line);
  background:var(--surface);
}
.keyspace-explainer,.keyspace-calculator{padding:25px}
.keyspace-calculator{border-left:1px solid var(--line)}
.keyspace-explainer h3,.keyspace-calculator h3{font-size:1.45rem}
.keyspace-explainer dl{
  margin:18px 0;
  border-top:1px solid var(--line-soft);
}
.keyspace-explainer dl div{
  display:flex;
  justify-content:space-between;
  gap:16px;
  padding:11px 0;
  border-bottom:1px solid var(--line-soft);
}
.keyspace-explainer dt{color:var(--muted)}
.keyspace-explainer dd{margin:0;font-weight:800}
.keyspace-explainer .key-total{
  display:block;
  padding:16px 0;
}
.key-total dd{
  margin-top:6px;
  font-family:Georgia,"Times New Roman",serif;
  font-size:clamp(1.45rem,3vw,2.25rem);
  color:var(--accent-dark);
  overflow-wrap:anywhere;
}
.security-note{
  margin:18px 0 0;
  padding:12px 14px;
  border-left:4px solid #8a6620;
  background:#f5eedc;
  color:#51431e;
}
.rate-presets{
  display:flex;
  flex-wrap:wrap;
  gap:8px;
  margin:10px 0 0;
}
.preset-btn{
  min-height:44px;
  padding:8px 11px;
  border:1px solid var(--control-line);
  border-radius:var(--radius-sm);
  background:#fff;
  color:var(--accent-dark);
  font-weight:700;
}
.preset-btn:hover{background:var(--soft-green)}
.calculation-result{
  margin:18px 0 0;
  border-top:1px solid var(--line);
}
.calculation-result div{
  display:grid;
  grid-template-columns:minmax(0,1fr) minmax(150px,.7fr);
  gap:14px;
  padding:12px 0;
  border-bottom:1px solid var(--line-soft);
}
.calculation-result dt{color:var(--muted)}
.calculation-result dd{margin:0;font-weight:800;text-align:right}

.presentation-section{border-bottom:0}
.demo-sequence{
  margin:0;
  padding:0;
  list-style:none;
  border-top:1px solid var(--line);
}
.demo-sequence li{
  display:grid;
  grid-template-columns:52px minmax(0,1fr);
  gap:18px;
  padding:16px 0;
  border-bottom:1px solid var(--line-soft);
}
.demo-sequence>li>span{
  font-family:Georgia,"Times New Roman",serif;
  color:var(--accent-dark);
  font-size:1.45rem;
}
.demo-sequence strong{display:block;margin-bottom:3px}
.demo-sequence p{margin:0;color:var(--muted)}

footer{
  border-top:1px solid var(--line);
  background:var(--surface);
  padding:26px 20px 38px;
}
footer p{
  width:min(1160px,100%);
  margin:auto;
  color:var(--muted);
  font-size:.84rem;
}

@media(max-width:900px){
  .masthead{
    grid-template-columns:1fr;
    gap:34px;
    padding-top:48px;
  }
  .required-vector{max-width:620px}
  .workbench,.security-layout{grid-template-columns:1fr}
  .work-panel+.work-panel,.keyspace-calculator{border-left:0;border-top:1px solid var(--line)}
  .concept-note{grid-template-columns:1fr;gap:14px}
  .key-order-block{grid-template-columns:1fr}
  .key-order-block>div+div{border-left:0;border-top:1px solid var(--line)}
}

@media(max-width:720px){
  .nav-shell,main{width:min(100% - 28px,1160px)}
  .desktop-nav{display:none}
  .mobile-nav{display:block}
  h1{font-size:clamp(2.45rem,12vw,3.9rem)}
  .masthead{padding:38px 0 42px}
  .lesson-section{padding:42px 0}
  .section-intro{grid-template-columns:44px minmax(0,1fr);gap:12px}
  .section-number{font-size:1.55rem}
  .two-field-row,.schedule-controls,.process-list{grid-template-columns:1fr}
  .process-list li:nth-child(odd){border-right:0}
  .work-panel,.schedule-input,.test-toolbar,.keyspace-explainer,.keyspace-calculator{padding:20px 16px}
  .test-toolbar{align-items:flex-start;flex-direction:column}
  .test-actions{width:100%;align-items:stretch;flex-direction:column}
  .test-actions .btn{width:100%}
  .split-stage{grid-template-columns:1fr}
  .split-stage div+div{border-left:0;border-top:1px solid var(--line);margin-top:10px;padding-top:10px}
  .validation-list div{grid-template-columns:1fr;gap:4px}
  .calculation-result div{grid-template-columns:1fr;gap:4px}
  .calculation-result dd{text-align:left}
  .output-label{align-items:flex-start}
  .vector-data div{grid-template-columns:1fr;gap:2px}
}

@media(max-width:420px){
  .nav-shell,main{width:min(100% - 20px,1160px)}
  .section-intro{grid-template-columns:1fr}
  .section-number{font-size:1rem;font-weight:800}
  .work-panel{padding:18px 13px}
  .keyspace-explainer,.keyspace-calculator{padding:18px 14px}
  .demo-sequence li{grid-template-columns:36px minmax(0,1fr);gap:10px}
}