:root{
  --paper:#F3F4F8;
  --surface:#FFFFFF;
  --raise:#FBFBFE;
  --ink:#17161F;
  --muted:#5C5B6E;
  --rule:#E3E3EC;
  --grid:rgba(75,63,207,.055);
  --violet:#4B3FCF;
  --on-violet:#FFFFFF;
  --amber:#C9871F;
  --grow:#0E9C8B;
  --fade:#D2373C;
  --shadow:0 26px 60px -30px rgba(30,27,75,.34);
}
:root:not([data-theme="light"]){
  @media (prefers-color-scheme: dark){
    --paper:#100F17;
    --surface:#17161F;
    --raise:#1E1D28;
    --ink:#ECEBF4;
    --muted:#9B99AE;
    --rule:#2B2A38;
    --grid:rgba(255,255,255,.035);
    --violet:#8B81F3;
    --on-violet:#12111A;
    --amber:#E6A94C;
    --grow:#2FBBA9;
    --fade:#E75A5F;
    --shadow:0 26px 60px -30px rgba(0,0,0,.62);
  }
}
:root[data-theme="dark"]{
  --paper:#100F17;
  --surface:#17161F;
  --raise:#1E1D28;
  --ink:#ECEBF4;
  --muted:#9B99AE;
  --rule:#2B2A38;
  --grid:rgba(255,255,255,.035);
  --violet:#8B81F3;
  --on-violet:#12111A;
  --amber:#E6A94C;
  --grow:#2FBBA9;
  --fade:#E75A5F;
  --shadow:0 26px 60px -30px rgba(0,0,0,.62);
}

*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{
  margin:0;
  font-family:"Public Sans", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  font-size:16px;
  line-height:1.65;
  color:var(--ink);
  background-color:var(--paper);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size:30px 30px;
  background-position:-1px -1px;
}
::selection{background:var(--violet);color:var(--on-violet)}

h1,h2,h3{font-family:"Fraunces", Georgia, "Times New Roman", serif;font-weight:500;text-wrap:balance;margin:0}
h1{font-size:clamp(2.4rem, 1.4rem + 3.6vw, 4rem);line-height:1.02;letter-spacing:-.02em}
h2{font-size:clamp(1.85rem, 1.3rem + 2vw, 2.7rem);line-height:1.08;letter-spacing:-.015em}
h3{font-family:"Public Sans", sans-serif;font-weight:700;font-size:1.05rem;line-height:1.35;letter-spacing:-.005em}
p{margin:0}
a{color:inherit}

.wrap{max-width:1080px;margin:0 auto;padding-inline:clamp(20px, 5vw, 40px)}
.mono{font-family:"JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace}

/* ---------- nav ---------- */
.nav{
  position:sticky;top:0;z-index:20;
  border-bottom:1px solid var(--rule);
  background:color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter:saturate(1.4) blur(10px);
}
.nav-inner{display:flex;align-items:center;justify-content:space-between;height:62px}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none;font-family:"Fraunces",serif;font-weight:600;font-size:1.3rem;letter-spacing:-.01em}
.brand-icon{width:26px;height:26px;flex:none;border-radius:6px;box-shadow:0 0 0 1px var(--rule)}
.brand-word{display:flex;align-items:baseline;gap:9px;font-weight:inherit}
.brand span{font-family:"JetBrains Mono",monospace;font-size:.62rem;font-weight:400;color:var(--muted);letter-spacing:.04em}
.nav-links{display:flex;gap:26px}
.nav-links a{text-decoration:none;color:var(--muted);font-size:.9rem;font-weight:500}
.nav-links a:hover{color:var(--ink)}
@media (max-width:760px){.nav-links{display:none}}
.nav-end{display:flex;align-items:center;gap:14px}
.lang{display:flex;gap:2px;font-family:"JetBrains Mono",monospace;font-size:.74rem;letter-spacing:.04em}
.lang a{padding:4px 6px;border-radius:6px;color:var(--muted);text-decoration:none}
.lang a:hover{color:var(--ink)}
.lang a[aria-current]{color:var(--ink);font-weight:500}
.lang a{display:inline-flex;align-items:center;gap:5px}
.lang svg{width:16px;height:12px;flex:none;border-radius:2px;box-shadow:0 0 0 1px var(--rule)}
.lang a:not([aria-current]) svg{opacity:.55}
.lang a:hover svg{opacity:1}
@media (max-width:400px){.lang .code{position:absolute;width:1px;height:1px;overflow:hidden;clip-path:inset(50%);white-space:nowrap}.lang{gap:6px}}
.nav .store-btn b{white-space:nowrap}
@media (max-width:480px){.brand span{display:none}}

/* ---------- shared section rhythm ---------- */
section{scroll-margin-top:80px}
.band{border-top:1px solid var(--rule);padding-block:clamp(44px, 5vw, 72px)}
.eyebrow{font-family:"JetBrains Mono",monospace;font-size:.74rem;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);display:block;margin-bottom:14px}
.eyebrow b{color:var(--violet);font-weight:500}
.eyebrow.sig b{color:var(--amber)}
.prose{max-width:64ch}
.prose p + p{margin-top:1rem}
.prose em{font-style:italic;color:var(--ink)}

/* ---------- hero ---------- */
.hero{padding-block:clamp(44px, 5vw, 76px) clamp(52px, 6vw, 88px)}
.hero-grid{display:grid;grid-template-columns:minmax(300px, 360px) minmax(0,1fr);gap:clamp(32px, 5vw, 60px);align-items:start}
.hero-grid .builder-side{grid-column:1;grid-row:1}
.hero-grid .hero-copy{grid-column:2;grid-row:1}
@media (max-width:940px){
  .hero-grid{grid-template-columns:1fr}
  .hero-grid .builder-side,.hero-grid .hero-copy{grid-column:auto;grid-row:auto}
}
.hero .kicker{font-family:"JetBrains Mono",monospace;font-size:.78rem;letter-spacing:.1em;text-transform:uppercase;color:var(--amber);margin-bottom:18px}
.hero p.lead{font-size:1.18rem;line-height:1.55;color:var(--ink);margin-top:20px;max-width:34ch}
.hero p.lead b{font-weight:600}
.cta-row{display:flex;flex-wrap:wrap;gap:12px;margin-top:26px}
.note{margin-top:16px;font-size:.86rem;color:var(--muted)}
.promises{list-style:none;margin:28px 0 0;padding:16px 18px;display:flex;flex-direction:column;gap:14px;background:var(--surface);border:1px solid var(--rule);border-radius:16px}
.promises li{display:flex;gap:14px;align-items:flex-start}
.promises svg{flex:none;width:22px;height:22px;margin-top:2px;fill:none;stroke:var(--violet);stroke-width:2;stroke-linecap:round;stroke-linejoin:round}
.promises b{display:block;font-size:.95rem;font-weight:600}
.promises span{font-size:.86rem;line-height:1.45;color:var(--muted)}
.promises b{color:var(--ink)}

.store-btn{display:inline-flex;align-items:center;gap:10px;text-decoration:none;padding:9px 16px;border-radius:11px;background:var(--ink);color:var(--paper);border:1px solid transparent}
.store-btn svg{width:19px;height:19px;flex:none;fill:currentColor}
.store-btn .t{display:flex;flex-direction:column;line-height:1.15;text-align:left}
.store-btn .t small{font-size:.58rem;font-weight:600;letter-spacing:.06em;text-transform:uppercase;opacity:.72}
.store-btn .t b{font-size:.98rem;font-weight:700}

/* ---------- builder ---------- */
.builder{
  background:var(--surface);
  border:1px solid var(--rule);
  border-radius:16px;
  padding:20px;
  box-shadow:var(--shadow);
}
.builder-head{display:flex;align-items:baseline;justify-content:space-between;gap:10px;margin-bottom:4px}
.builder-head h3{font-family:"Fraunces",serif;font-weight:500;font-size:1.15rem}
.builder-head .tag{font-family:"JetBrains Mono",monospace;font-size:.66rem;color:var(--muted);letter-spacing:.05em}
.builder label{display:block;font-family:"JetBrains Mono",monospace;font-size:.68rem;letter-spacing:.09em;text-transform:uppercase;color:var(--muted);margin-top:14px}
.builder input[type=text],
.builder input[type=date]{
  width:100%;max-width:420px;margin-top:6px;padding:9px 11px;
  font:inherit;font-size:.92rem;
  color:var(--ink);background:var(--raise);
  border:1px solid var(--rule);border-radius:9px;
}
.builder input::placeholder,
.builder textarea::placeholder{color:color-mix(in srgb, var(--muted) 80%, transparent)}
.builder label.check{display:flex;align-items:center;gap:9px;margin-top:16px;font-family:"Public Sans",system-ui,sans-serif;font-size:.9rem;letter-spacing:0;text-transform:none;color:var(--ink);cursor:pointer}
.builder label.check input{width:auto;margin:0;accent-color:var(--violet)}
.cards-list{margin-top:12px;display:flex;flex-direction:column;gap:8px}
.card-row{display:flex;gap:8px;align-items:flex-start}
.card-row textarea{flex:1;padding:9px 11px;font:inherit;font-size:.92rem;line-height:1.4;color:var(--ink);background:var(--raise);border:1px solid var(--rule);border-radius:9px;min-width:0;resize:none;overflow:hidden;display:block}
.remove-btn{flex:none;width:36px;height:36px;display:inline-flex;align-items:center;justify-content:center;font-size:1.1rem;line-height:1;color:var(--fade);background:transparent;border:1px solid var(--rule);border-radius:8px;cursor:pointer}
.remove-btn:hover{background:color-mix(in srgb, var(--fade) 12%, transparent);border-color:color-mix(in srgb, var(--fade) 40%, var(--rule))}

/* answer column: the answer, then a quiz card's wrong answers */
.answer-col{flex:1;min-width:0;display:flex;flex-direction:column;gap:6px}
.opt-line{display:flex;gap:6px;align-items:flex-start}
.opt-mark{flex:none;width:16px;margin-top:9px;text-align:center;font-weight:800;font-size:.9rem;line-height:1.4}
.opt-mark--right{color:var(--grow)}
.opt-mark--wrong{color:var(--fade)}
.wrong-remove{flex:none;width:28px;height:28px;margin-top:5px;display:inline-flex;align-items:center;justify-content:center;font-size:.95rem;line-height:1;color:var(--muted);background:transparent;border:1px solid transparent;border-radius:7px;cursor:pointer}
.wrong-remove:hover{color:var(--fade);border-color:var(--rule)}
.add-wrong{align-self:flex-start;margin-left:22px;padding:2px 0;font:inherit;font-size:.78rem;color:var(--muted);background:none;border:none;cursor:pointer}
.add-wrong:hover{color:var(--ink);text-decoration:underline}
.card-row:not(.card-row--quiz) .add-wrong{margin-left:0}

/* card field: Markdown/LaTeX preview with click-to-edit */
.card-field{position:relative;flex:1;min-width:0}
.card-field textarea{width:100%}
.card-preview{
  padding:9px 11px;font-size:.92rem;line-height:1.5;
  color:var(--ink);background:var(--raise);
  border:1px solid var(--rule);border-radius:9px;
  min-height:38px;overflow-x:auto;cursor:text;
}
.card-preview:hover{border-color:color-mix(in srgb, var(--violet) 35%, var(--rule))}

/* preview / edit toggle switch */
.builder label.switch{display:inline-flex;align-items:center;gap:10px;margin:0;cursor:pointer;user-select:none;font-family:"Public Sans",system-ui,sans-serif;font-size:.9rem;font-weight:500;letter-spacing:0;text-transform:none;color:var(--ink)}
.switch input{position:absolute;width:1px;height:1px;opacity:0;margin:0}
.switch-track{position:relative;flex:none;width:40px;height:22px;border-radius:999px;background:var(--rule);border:1px solid var(--rule);transition:background .15s ease,border-color .15s ease}
.switch-thumb{position:absolute;top:2px;left:2px;width:16px;height:16px;border-radius:50%;background:var(--surface);box-shadow:0 1px 3px rgba(0,0,0,.3);transition:transform .15s ease}
.switch input:checked + .switch-track{background:var(--violet);border-color:var(--violet)}
.switch input:checked + .switch-track .switch-thumb{transform:translateX(18px)}
.switch input:focus-visible + .switch-track{outline:2px solid var(--violet);outline-offset:2px}
.card-preview > :first-child{margin-top:0}
.card-preview > :last-child{margin-bottom:0}
.card-preview p{margin:0 0 .5em}
.card-preview ul,.card-preview ol{margin:.3em 0;padding-left:1.4em}
.card-preview code{font-family:"JetBrains Mono",monospace;font-size:.88em;background:color-mix(in srgb, var(--muted) 16%, transparent);padding:1px 4px;border-radius:4px}
.card-preview pre{background:color-mix(in srgb, var(--muted) 12%, transparent);padding:8px 10px;border-radius:7px;overflow-x:auto}
.card-preview pre code{background:none;padding:0}
.card-preview .preview-empty{color:var(--muted);font-family:"JetBrains Mono",monospace;font-size:.72rem}
.card-preview .katex-display{margin:.4em 0}

.builder-side{
  background:var(--surface);
  border:1px solid var(--rule);
  border-radius:16px;
  padding:20px;
  box-shadow:var(--shadow);
  align-self:start;
}
.builder-side .btn{width:100%;margin-top:14px}
.builder-side .qr-preview{flex-direction:column;align-items:center;gap:12px}
.builder-side .qr-side{width:100%}
#builder{margin-top:clamp(28px, 4vw, 44px)}
.builder-controls{display:flex;flex-wrap:wrap;align-items:center;gap:8px 16px;margin-top:16px}
.btn{appearance:none;font:inherit;font-weight:600;font-size:.88rem;padding:9px 14px;border-radius:9px;border:1px solid transparent;cursor:pointer;background:var(--violet);color:var(--on-violet)}
.btn:hover{filter:brightness(1.06)}
.btn--ai{background:var(--ink);color:var(--paper)}
.btn--add{background:transparent;color:var(--grow);border-color:color-mix(in srgb, var(--grow) 55%, var(--rule))}
.btn--add:hover{background:color-mix(in srgb, var(--grow) 12%, transparent);filter:none}
.builder-hint{margin-top:10px;font-family:"JetBrains Mono",monospace;font-size:.68rem;line-height:1.5;color:var(--muted)}
.builder-hint b{color:var(--ink);font-weight:500}
.paste-msg{margin-top:10px;padding:10px 12px;border-radius:9px;font-size:.8rem;line-height:1.5;color:var(--ink);background:color-mix(in srgb, var(--amber) 15%, var(--surface));border:1px solid color-mix(in srgb, var(--amber) 45%, var(--rule))}
.paste-msg code{font-family:"JetBrains Mono",monospace;font-size:.9em;background:color-mix(in srgb, var(--amber) 22%, var(--surface));padding:1px 5px;border-radius:5px}

.qr-preview{display:flex;gap:14px;align-items:center}
#qrcodes{
  position:relative;width:200px;height:200px;flex:none;
  background:#fff;border-radius:14px;
  box-shadow:
    0 0 0 1px color-mix(in srgb, var(--amber) 45%, var(--rule)),
    0 14px 32px -18px rgba(30,27,75,.35);
}
/* inset creates even padding between the white plate and the code */
.qr-frame{position:absolute;inset:14px;display:none;align-items:center;justify-content:center}
.qr-canvas img,.qr-canvas canvas{display:block;width:172px;height:172px}
.qr-side{flex:1;min-width:0}
.qr-side .lead-sm{font-size:.82rem;color:var(--ink)}
#qrInfo{margin-top:8px;font-family:"JetBrains Mono",monospace;font-size:.66rem;color:var(--muted)}
@media (max-width:420px){
  #qrcodes{width:180px;height:180px}
  .qr-canvas img,.qr-canvas canvas{width:152px;height:152px}
}

/* ---------- concept lists ---------- */
.tags{display:flex;flex-wrap:wrap;gap:8px;margin-top:22px;list-style:none;padding:0}
.tags li{font-family:"JetBrains Mono",monospace;font-size:.72rem;color:var(--muted);border:1px solid var(--rule);border-radius:999px;padding:4px 11px}

/* ---------- spaced repetition chart ---------- */
.chart-block{display:grid;grid-template-columns:minmax(0,1fr) minmax(280px, 540px);gap:clamp(28px,4vw,52px);align-items:start;margin-top:24px}
@media (max-width:900px){.chart-block{grid-template-columns:1fr}}
.chart-figure{margin:0}
.chart{display:block;width:100%;height:auto}
.chart .grid{stroke:var(--rule);stroke-width:1}
.chart .axis{stroke:var(--muted);stroke-width:1.5}
.chart .once{fill:none;stroke:var(--fade);stroke-width:2.5;stroke-dasharray:2 6;stroke-linecap:round}
.chart .spaced{fill:none;stroke:var(--violet);stroke-width:3;stroke-linejoin:round}
.chart .rev{fill:var(--amber);stroke:var(--surface);stroke-width:2}
.chart text{fill:var(--muted);font-family:"JetBrains Mono",monospace;font-size:11px}
.legend{list-style:none;margin:16px 0 0;padding:0;display:flex;flex-direction:column;gap:8px;font-family:"JetBrains Mono",monospace;font-size:.72rem;color:var(--muted)}
.legend li{display:flex;align-items:center;gap:10px}
.legend .sw{flex:none;width:26px;height:0;border-top-width:3px;border-top-style:solid}
.legend .sw.once{border-top-style:dashed;border-color:var(--fade)}
.legend .sw.spaced{border-color:var(--violet)}
.legend .dot{flex:none;width:10px;height:10px;border-radius:50%;background:var(--amber)}

/* ---------- steps ---------- */
.steps{list-style:none;counter-reset:step;margin:28px 0 0;padding:0;display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:24px}
.steps li{counter-increment:step;display:flex;flex-direction:column;gap:8px}
.steps li::before{content:counter(step,decimal-leading-zero);font-family:"JetBrains Mono",monospace;font-size:1.5rem;color:var(--violet);line-height:1}
.steps li:nth-child(3)::before{color:var(--amber)}
.steps p{font-size:.92rem;color:var(--muted)}
.step-cta{margin-top:26px;display:inline-flex;align-items:center;gap:8px;font-weight:600;font-size:.9rem;text-decoration:none;color:var(--violet)}
.step-cta:hover{text-decoration:underline}

/* ---------- copyable AI prompts ---------- */
.prompts{margin-top:14px;display:flex;flex-direction:column;gap:10px}
.prompt{border:1px solid var(--rule);border-radius:12px;background:var(--surface)}
.prompt summary{cursor:pointer;list-style:none;display:flex;justify-content:space-between;align-items:center;gap:12px;padding:12px 14px;font-weight:600;font-size:.92rem}
.prompt summary::-webkit-details-marker{display:none}
.prompt summary::after{content:"+";font-family:"JetBrains Mono",monospace;color:var(--muted)}
.prompt[open] summary::after{content:"–"}
.prompt summary small{display:block;font-weight:400;font-size:.78rem;color:var(--muted);margin-top:2px}
.prompt-body{position:relative;padding:0 12px 12px}
.prompt pre{margin:0;padding:12px 40px 12px 12px;border-radius:9px;background:var(--raise);border:1px solid var(--rule);font-family:"JetBrains Mono",monospace;font-size:.72rem;line-height:1.55;color:var(--ink);white-space:pre-wrap;overflow-wrap:anywhere}
.prompt-hint{margin-top:8px;font-size:.78rem;line-height:1.45;color:var(--muted)}
.copy-prompt{position:absolute;top:6px;right:18px;display:grid;place-items:center;width:30px;height:30px;padding:0;border-radius:7px;border:1px solid var(--rule);background:var(--surface);color:var(--muted);cursor:pointer;opacity:0;transition:opacity .15s}
.copy-prompt:hover{color:var(--ink)}
.copy-prompt svg{width:16px;height:16px;fill:none;stroke:currentColor;stroke-width:2;stroke-linecap:round;stroke-linejoin:round}
.copy-prompt .i-done{display:none}
.copy-prompt.copied{color:var(--grow);opacity:1}
.copy-prompt.copied .i-copy{display:none}
.copy-prompt.copied .i-done{display:block}
.prompt-body:hover .copy-prompt,.copy-prompt:focus-visible{opacity:1}
@media (hover:none){.copy-prompt{opacity:1}}

/* ---------- features ---------- */
.features{display:grid;grid-template-columns:repeat(auto-fit,minmax(288px,1fr));gap:16px;margin-top:28px}
.feature{background:var(--surface);border:1px solid var(--rule);border-radius:13px;padding:18px}
.feature .fi{font-family:"JetBrains Mono",monospace;font-size:.7rem;color:var(--amber);letter-spacing:.06em}
.feature h3{margin:10px 0 6px}
.feature p{font-size:.88rem;color:var(--muted)}
.new-tag{display:inline-block;margin-left:8px;padding:2px 7px;border-radius:999px;vertical-align:3px;font-family:"JetBrains Mono",monospace;font-size:.62rem;font-weight:600;letter-spacing:.06em;text-transform:uppercase;color:var(--on-violet);background:var(--violet)}

/* ---------- faq ---------- */
.faq{margin-top:24px;max-width:70ch}
.faq details{border-top:1px solid var(--rule);padding:14px 0}
.faq details:last-child{border-bottom:1px solid var(--rule)}
.faq summary{cursor:pointer;font-weight:600;list-style:none;display:flex;justify-content:space-between;gap:16px}
.faq summary::-webkit-details-marker{display:none}
.faq summary::after{content:"+";font-family:"JetBrains Mono",monospace;color:var(--muted)}
.faq details[open] summary::after{content:"–"}
.faq p{margin-top:10px;font-size:.92rem;color:var(--muted)}

/* ---------- closing cta ---------- */
.closing{text-align:center}
.closing h2{margin-bottom:20px}
.closing .cta-row{justify-content:center}
.closing .store-btn{border-radius:0}
.closing .stamp{margin-top:20px;font-family:"JetBrains Mono",monospace;font-size:.7rem;letter-spacing:.14em;text-transform:uppercase;color:var(--muted)}

footer{border-top:1px solid var(--rule);padding-block:32px;font-size:.82rem;color:var(--muted)}
.foot-inner{display:flex;flex-wrap:wrap;gap:16px 28px;align-items:center;justify-content:space-between}
footer a{color:var(--muted);text-decoration:none}
footer a:hover{color:var(--ink)}

a:focus-visible,button:focus-visible,summary:focus-visible,input:focus-visible{outline:2px solid var(--violet);outline-offset:2px;border-radius:6px}

@media (prefers-reduced-motion: reduce){
  *{transition:none !important;animation:none !important}
}