/* =====================================================================
   Statistics — First Principles · mobile-first lesson deck
   "paper" aesthetic · Fraunces + Spline Sans Mono · light theme
   ===================================================================== */
:root{
  --paper:#faf8f2;
  --paper-2:#f1ede3;
  --card:#ffffff;
  --ink:#18211f;
  --ink-soft:#5a635f;
  --line:#e2ddd1;
  --accent:#0f7173;
  --accent-soft:#9cc7c5;
  --accent-2:#d97742;
  --blue:#16484f;
  --radius:14px;
  --shadow:4px 4px 0 rgba(24,33,31,.12);
  --shadow-lg:5px 5px 0 rgba(24,33,31,.13);
  --top:52px;
  --nav:70px;
}

*{box-sizing:border-box;margin:0;padding:0;min-width:0}
html{height:100%;color-scheme:light;background:var(--paper);-webkit-text-size-adjust:100%}
body{
  height:100dvh;
  width:100%;
  max-width:100%;
  overflow:hidden;
  overscroll-behavior:none;
  background:var(--paper);
  color:var(--ink);
  font-family:'Spline Sans Mono',monospace;
  line-height:1.55;
  -webkit-font-smoothing:antialiased;
  background-image:
    radial-gradient(circle at 12% 8%, rgba(15,113,115,.05), transparent 38%),
    radial-gradient(circle at 92% 96%, rgba(217,119,66,.05), transparent 42%);
}
/* subtle paper grain */
body::before{
  content:"";position:fixed;inset:0;pointer-events:none;z-index:0;opacity:.5;
  background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='120' height='120'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='0.035'/%3E%3C/svg%3E");
}
button{font-family:inherit;cursor:pointer;color:inherit}
img,canvas,svg{max-width:100%}

/* ---------- focus & skip link (keyboard a11y) ---------- */
:focus{outline:none}
:focus-visible{outline:3px solid var(--accent-2);outline-offset:2px;border-radius:6px}
.lesson-title:focus-visible{outline-offset:4px}
input[type=range]:focus-visible{outline:3px solid var(--accent-2);outline-offset:4px}
.skip-link{
  position:fixed;top:8px;left:50%;transform:translate(-50%,-160%);z-index:40;
  background:var(--ink);color:var(--paper);font-size:.8rem;font-weight:600;
  padding:9px 16px;border-radius:10px;text-decoration:none;
  transition:transform .18s;
}
.skip-link:focus{transform:translate(-50%,0)}

/* ============ APP SHELL ============ */
.app{
  position:relative;z-index:1;
  height:100dvh;width:100%;
  max-width:520px;margin:0 auto;
  display:grid;
  grid-template-rows:var(--top) 1fr var(--nav);
  overflow:hidden;
  padding:0 14px;
  padding-top:env(safe-area-inset-top);
  padding-bottom:env(safe-area-inset-bottom);
}

/* ---------- TOP BAR ---------- */
.topbar{display:flex;align-items:center;gap:12px;height:var(--top);min-width:0}
.brand{font-family:'Fraunces',serif;font-weight:900;font-size:1rem;letter-spacing:-.01em;white-space:nowrap;flex:none}
.brand em{font-style:italic;font-weight:500;color:var(--accent)}
.progress{flex:1;min-width:0;height:6px;border-radius:99px;background:var(--paper-2);border:1.5px solid var(--ink);overflow:hidden}
.progress > i{display:block;height:100%;width:0;background:var(--accent);transition:width .4s cubic-bezier(.22,1,.36,1)}
.menu-btn{
  width:38px;height:38px;flex:none;
  border:1.5px solid var(--ink);border-radius:10px;background:var(--card);
  box-shadow:2px 2px 0 rgba(24,33,31,.14);
  display:grid;place-items:center;transition:transform .12s, background .2s;
}
.menu-btn:active{transform:translate(2px,2px);box-shadow:none}
.menu-btn span{display:block;width:16px;height:2px;background:var(--ink);border-radius:2px;margin:2px 0}

/* ---------- STAGE (one lesson at a time) ---------- */
.stage{position:relative;overflow:hidden;min-height:0;min-width:0}
.lesson{
  position:absolute;inset:0;
  overflow-y:auto;overflow-x:hidden;
  -webkit-overflow-scrolling:touch;overscroll-behavior:contain;
  padding:4px 2px 10px;
  display:flex;flex-direction:column;gap:14px;
  animation:slide-in .42s cubic-bezier(.22,1,.36,1) both;
}
.lesson.from-left{animation-name:slide-in-left}
@keyframes slide-in{from{opacity:0;transform:translateX(30px)}to{opacity:1;transform:none}}
@keyframes slide-in-left{from{opacity:0;transform:translateX(-30px)}to{opacity:1;transform:none}}

.lesson-head{display:flex;align-items:baseline;gap:11px;min-width:0}
.tag{font-family:'Fraunces',serif;font-weight:900;font-size:2rem;line-height:.9;color:var(--accent-2);flex:none}
.lesson-head > span{min-width:0}
.lesson-title{display:block;font-family:'Fraunces',serif;font-weight:600;font-size:1.5rem;line-height:1.05;letter-spacing:-.01em}
.lesson-sub{display:block;font-size:.68rem;letter-spacing:.14em;text-transform:uppercase;color:var(--ink-soft);margin-top:3px}
.body{color:var(--ink-soft);font-size:.92rem}
.body strong{color:var(--ink);font-weight:600}

/* ---------- shared lesson components ---------- */
.card{background:var(--card);border:1.5px solid var(--ink);border-radius:var(--radius);padding:16px 14px;box-shadow:var(--shadow-lg)}
.card h3{font-family:'Fraunces',serif;font-weight:600;font-size:1rem;margin-bottom:3px}
.hint{font-size:.74rem;color:var(--ink-soft);margin-bottom:13px}
.caption{font-size:.72rem;color:var(--ink-soft);margin-top:10px;text-align:center}
.caption b{color:var(--ink);font-weight:600}

.definition{
  background:var(--paper-2);border:1.5px solid var(--ink);border-left:5px solid var(--accent);
  border-radius:var(--radius);padding:13px 15px;
  font-family:'Fraunces',serif;font-style:italic;font-size:.98rem;line-height:1.5;color:var(--ink);
  box-shadow:var(--shadow);
}
.definition b{font-style:normal;font-weight:600;color:var(--accent)}

.stats-out{display:grid;grid-template-columns:repeat(3,1fr);gap:8px;margin-top:15px}
.stat{border:1.5px solid var(--line);border-radius:10px;padding:9px 4px;text-align:center;background:var(--paper);min-width:0}
.stat .k{font-size:.6rem;letter-spacing:.08em;text-transform:uppercase;color:var(--ink-soft);white-space:nowrap}
.stat .v{font-family:'Fraunces',serif;font-size:1.4rem;font-weight:600;color:var(--accent);line-height:1.1;margin-top:2px;white-space:nowrap}
.stat.alt .v{color:var(--blue)}

.controls{display:flex;gap:8px;margin-top:14px;flex-wrap:wrap}
.btn{
  font-family:'Spline Sans Mono',monospace;font-weight:600;font-size:.76rem;
  background:var(--ink);color:var(--paper);border:1.5px solid var(--ink);
  padding:10px 9px;border-radius:10px;letter-spacing:.01em;
  flex:1 1 auto;min-width:0;white-space:nowrap;
  transition:transform .1s, background .2s;
}
.btn:active{transform:translateY(2px)}
.btn.ghost{background:var(--card);color:var(--ink);box-shadow:2px 2px 0 rgba(24,33,31,.12)}
.btn.ghost:active{box-shadow:none}

.slider-row{display:flex;align-items:center;gap:11px;margin:11px 0 2px;font-size:.78rem;min-width:0}
.slider-row label{min-width:84px;flex:none;color:var(--ink-soft)}
input[type=range]{flex:1;min-width:0;accent-color:var(--accent);height:26px;cursor:pointer}
.slider-row output{min-width:52px;flex:none;text-align:right;font-weight:600;font-family:'Fraunces',serif;font-size:1.02rem}

.toggle-row{display:flex;align-items:center;gap:8px;margin-top:10px;font-size:.76rem;color:var(--ink-soft)}
.toggle-row input{width:17px;height:17px;accent-color:var(--accent)}

canvas{display:block;width:100%;height:auto;touch-action:pan-y;border-radius:6px}

/* central-tendency bars */
.dotfield{display:flex;flex-wrap:nowrap;gap:5px;align-items:flex-end;min-height:128px;border-bottom:2px solid var(--ink);padding-bottom:4px}
.bar{flex:1 1 0;min-width:0;background:var(--blue);border:1.5px solid var(--ink);border-bottom:none;border-radius:6px 6px 0 0;cursor:pointer;transition:height .25s ease, background .15s;display:flex;justify-content:center;align-items:flex-start}
.bar:active{background:var(--accent)}
.bar span{font-size:.64rem;color:var(--paper);margin-top:3px;font-weight:600}

/* spread viz */
.spread{position:relative;height:82px;border-bottom:2px solid var(--ink);margin-top:8px}
.pt{position:absolute;bottom:0;width:13px;height:13px;border-radius:50%;background:var(--blue);border:1.5px solid var(--ink);transform:translateX(-50%)}
.meanline{position:absolute;top:0;bottom:0;width:2px;background:var(--accent)}
.meanline::after{content:"x\0304";position:absolute;top:-18px;left:50%;transform:translateX(-50%);color:var(--accent);font-weight:600;font-size:.76rem}

.legend{display:flex;gap:13px;font-size:.68rem;color:var(--ink-soft);margin-top:8px;flex-wrap:wrap}
.legend i{display:inline-block;width:11px;height:11px;border-radius:3px;margin-right:4px;vertical-align:middle;border:1px solid var(--ink)}

/* data-type classifier (L1) */
.typegrid{display:grid;grid-template-columns:1fr 1fr;gap:8px;margin-top:4px}
.typetile{
  text-align:left;background:var(--paper);border:1.5px solid var(--line);border-radius:11px;
  padding:9px 11px;box-shadow:2px 2px 0 rgba(24,33,31,.08);min-width:0;
  transition:transform .1s, border-color .15s, background .15s;
}
.typetile:active{transform:translate(2px,2px);box-shadow:none}
.typetile.right{border-color:var(--accent);background:#eef6f5}
.typetile .tv{display:block;font-family:'Fraunces',serif;font-weight:600;font-size:.9rem;line-height:1.12;color:var(--ink)}
.typetile .tt{display:block;font-size:.66rem;letter-spacing:.06em;text-transform:uppercase;margin-top:5px;color:var(--ink-soft)}
.typetile.right .tt{color:var(--accent);font-weight:600}

/* ---------- BOTTOM NAV ---------- */
.navbar{display:flex;align-items:center;gap:10px;height:var(--nav);min-width:0}
.nav-btn{
  flex:none;width:50px;height:50px;border-radius:14px;
  border:1.5px solid var(--ink);background:var(--card);box-shadow:var(--shadow);
  display:grid;place-items:center;transition:transform .1s, opacity .2s, background .2s;
}
.nav-btn:active{transform:translate(2px,2px);box-shadow:none}
.nav-btn:disabled{opacity:.3;box-shadow:none;cursor:default}
.nav-btn svg{width:22px;height:22px;stroke:var(--ink);stroke-width:2.4;fill:none;stroke-linecap:round;stroke-linejoin:round}
.nav-btn.next{background:var(--accent);box-shadow:4px 4px 0 var(--blue)}
.nav-btn.next svg{stroke:var(--paper)}
.nav-btn.next:active{box-shadow:none}

.dots{flex:1;min-width:0;display:flex;justify-content:center;align-items:center;gap:1px;flex-wrap:wrap}
/* the button is a generous (~26px) transparent hit target; .dot-mark is the visible 8px circle */
.dot{flex:none;width:26px;height:26px;display:grid;place-items:center;border:none;background:none;padding:0;border-radius:50%;cursor:pointer}
.dot-mark{width:8px;height:8px;border-radius:50%;background:var(--line);transition:transform .2s, background .2s}
.dot.active .dot-mark{background:var(--accent);transform:scale(1.45)}
.dot.seen .dot-mark{background:var(--accent-soft)}

/* ---------- CONTENTS SHEET ---------- */
.scrim{position:fixed;inset:0;z-index:20;background:rgba(24,33,31,.45);opacity:0;pointer-events:none;transition:opacity .25s}
.scrim.open{opacity:1;pointer-events:auto}
.sheet{
  position:fixed;z-index:21;left:0;right:0;bottom:0;
  max-width:520px;margin:0 auto;
  background:var(--paper);border:1.5px solid var(--ink);border-radius:22px 22px 0 0;
  box-shadow:0 -8px 0 rgba(24,33,31,.12);
  padding:18px 16px calc(20px + env(safe-area-inset-bottom));
  transform:translateY(105%);transition:transform .32s cubic-bezier(.22,1,.36,1);
  max-height:82dvh;overflow-y:auto;
}
.sheet.open{transform:none}
.sheet h2{font-family:'Fraunces',serif;font-weight:900;font-size:1.3rem;margin-bottom:2px}
.sheet h2 em{font-style:italic;color:var(--accent);font-weight:500}
.sheet .sub{font-size:.74rem;color:var(--ink-soft);margin-bottom:16px}
.toc{list-style:none;display:flex;flex-direction:column;gap:8px}
.toc-item{
  display:flex;align-items:center;gap:12px;width:100%;text-align:left;
  background:var(--card);border:1.5px solid var(--ink);border-radius:12px;
  padding:11px 13px;box-shadow:2px 2px 0 rgba(24,33,31,.12);
  transition:transform .1s, background .15s;
}
.toc-item:active{transform:translate(2px,2px);box-shadow:none}
.toc-item.current{background:var(--paper-2);border-left:5px solid var(--accent)}
.toc-num{font-family:'Fraunces',serif;font-weight:900;color:var(--accent-2);font-size:1.05rem;min-width:24px;flex:none}
.toc-txt{display:flex;flex-direction:column;min-width:0}
.toc-txt b{font-family:'Fraunces',serif;font-weight:600;font-size:.96rem;line-height:1.1}
.toc-txt small{font-size:.66rem;color:var(--ink-soft);letter-spacing:.07em;text-transform:uppercase;margin-top:1px}

@media (prefers-reduced-motion: reduce){
  *{animation-duration:.001ms !important;transition-duration:.001ms !important}
  .skip-link{transition:none}
}
@media (min-height:760px){ :root{ --nav:78px } .lesson{gap:16px} }
@media (min-width:470px){ .lesson-title{font-size:1.62rem} .tag{font-size:2.25rem} }