/* ============================================================
   ML Study Notes — design system
   ============================================================ */
:root {
  --font-display: "Space Grotesk", system-ui, sans-serif;
  --font-body: "IBM Plex Sans", system-ui, sans-serif;
  --font-mono: "IBM Plex Mono", ui-monospace, monospace;

  --paper:      #FBFAF7;
  --paper-2:    #F4F1EA;
  --ink:        #15161C;
  --ink-soft:   #383B47;
  --muted:      #6E7280;
  --line:       #E7E2D7;
  --line-soft:  #EFEBE2;

  --code-bg:    #14161F;
  --code-fg:    #E6E8F0;
  --code-dim:   #7E8499;
  --code-line:  #262A38;

  /* phase palette */
  --blue:    #2563EB;
  --violet:  #7C3AED;
  --teal:    #0E9488;
  --magenta: #DB2777;
  --amber:   #C2620E;

  --accent: var(--blue);
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--paper-2);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

.ic { width: 1em; height: 1em; display: inline-block; vertical-align: -0.125em; flex: none; }

/* brand logo chip */
.logo-chip {
  background: #fff; border-radius: 9px;
  padding: 6px 11px; display: inline-flex; align-items: center;
  box-shadow: 0 1px 0 rgba(0,0,0,.04);
}
.logo-chip img { display: block; height: 24px; width: auto; }
.logo-chip.sm img { height: 19px; }

/* ---- phase accent helpers ---- */
[data-phase="A"] { --accent: var(--blue); }
[data-phase="B"] { --accent: var(--violet); }
[data-phase="C"] { --accent: var(--teal); }
[data-phase="D"] { --accent: var(--magenta); }
[data-phase="E"] { --accent: var(--amber); }

/* ============================================================
   Page shell
   ============================================================ */
.doc {
  --page-w: 820px;
  margin: 0 auto;
  padding: 40px 24px 120px;
}

.page {
  width: 100%;
  max-width: var(--page-w);
  margin: 0 auto 34px;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 4px;
  box-shadow: 0 1px 0 rgba(0,0,0,.02), 0 18px 40px -28px rgba(20,22,32,.30);
  overflow: hidden;
}

.page-pad { padding: 64px 68px; }

/* ============================================================
   Top bar (screen only)
   ============================================================ */
.topbar {
  position: sticky; top: 0; z-index: 40;
  display: flex; align-items: center; gap: 14px;
  max-width: var(--page-w, 820px);
  margin: 0 auto 26px;
  padding: 11px 18px;
  background: rgba(251,250,247,.86);
  backdrop-filter: blur(10px);
  border: 1px solid var(--line);
  border-radius: 999px;
}
.topbar .brand {
  display: flex; align-items: center; gap: 9px;
  font-family: var(--font-display);
  font-weight: 600; font-size: 14px; letter-spacing: -.01em;
}
.topbar .brand .dot {
  width: 22px; height: 22px; border-radius: 6px;
  display: grid; place-items: center; color: #fff;
  background: var(--ink); font-size: 13px;
}
.topbar .spacer { flex: 1; }
.topbar nav { display: flex; gap: 2px; flex-wrap: wrap; }
.topbar nav a {
  font-family: var(--font-mono); font-size: 11px;
  color: var(--muted); text-decoration: none;
  padding: 4px 7px; border-radius: 6px; line-height: 1;
}
.topbar nav a:hover { background: var(--paper-2); color: var(--ink); }
.topbar .print-btn {
  font-family: var(--font-display); font-weight: 600; font-size: 12.5px;
  display: inline-flex; align-items: center; gap: 6px;
  background: var(--ink); color: #fff; border: 0;
  padding: 8px 14px; border-radius: 999px; cursor: pointer;
}
.topbar .print-btn:hover { background: #000; }

/* ============================================================
   COVER
   ============================================================ */
.cover {
  position: relative;
  background: var(--ink);
  color: #F4F4F2;
  padding: 76px 72px 64px;
  overflow: hidden;
}
.cover::before {
  content: ""; position: absolute; inset: 0;
  background-image:
    linear-gradient(rgba(255,255,255,.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,.04) 1px, transparent 1px);
  background-size: 34px 34px;
  mask-image: radial-gradient(120% 90% at 80% 0%, #000 30%, transparent 75%);
}
.cover > * { position: relative; }
.cover-top {
  display: flex; align-items: center; gap: 12px;
  font-family: var(--font-mono); font-size: 12.5px; letter-spacing: .12em;
  text-transform: uppercase; color: #B7BAD0;
}
.cover-top .pill {
  display: inline-flex; align-items: center; gap: 7px;
  border: 1px solid rgba(255,255,255,.18); border-radius: 999px;
  padding: 6px 13px; color: #fff;
}
.cover-top .pill .ic { color: #8FA6FF; }
.cover-mark {
  margin: 52px 0 0; display: flex; align-items: center; gap: 16px;
}
.cover-mark .glyph {
  width: 60px; height: 60px; border-radius: 15px;
  display: grid; place-items: center; flex: none;
  background: linear-gradient(150deg, #6E8BFF, #3B5BDB);
  color: #fff; font-size: 30px;
  box-shadow: 0 12px 30px -10px rgba(110,139,255,.6);
}
.cover h1 {
  font-family: var(--font-display);
  font-weight: 600; letter-spacing: -.03em; line-height: .98;
  font-size: 76px; margin: 0;
}
.cover .sub {
  font-family: var(--font-display); font-weight: 500;
  font-size: 26px; color: #C9CCDF; margin: 6px 0 0; letter-spacing: -.01em;
}
.cover .rule { height: 1px; background: rgba(255,255,255,.14); margin: 40px 0 26px; }
.cover .meta-row {
  display: flex; flex-wrap: wrap; gap: 26px 40px; align-items: flex-start;
}
.cover .meta-col .k {
  font-family: var(--font-mono); font-size: 11px; letter-spacing: .12em;
  text-transform: uppercase; color: #898DA8; margin-bottom: 6px;
}
.cover .meta-col .v {
  font-size: 15px; color: #EDEDF2; max-width: 320px;
}
.cover .meta-col .v b { color: #fff; font-weight: 600; }
.topics { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 40px; }
.topics .chip {
  font-family: var(--font-mono); font-size: 12px;
  border: 1px solid rgba(255,255,255,.16); border-radius: 7px;
  padding: 6px 11px; color: #D6D8E6; background: rgba(255,255,255,.03);
}
.cover .arc {
  margin-top: 38px; display: inline-flex; align-items: center; gap: 10px;
  font-family: var(--font-display); font-weight: 600; font-size: 18px; color: #fff;
}
.cover .arc .ic { color: #8FA6FF; }
.cover-contact {
  margin-top: 30px; padding-top: 22px; border-top: 1px solid rgba(255,255,255,.14);
  display: flex; flex-wrap: wrap; gap: 10px 28px;
  font-size: 14px; color: #C9CCDF;
}
.cover-contact span { display: inline-flex; align-items: center; gap: 8px; }
.cover-contact .ic { color: #8FA6FF; font-size: 16px; }
.cover-contact b { color: #fff; font-weight: 600; }

.closing-contact {
  margin-top: 16px; display: flex; flex-wrap: wrap; justify-content: center;
  gap: 8px 24px; font-size: 14px; color: var(--ink-soft);
}
.closing-contact span { display: inline-flex; align-items: center; gap: 7px; }
.closing-contact .ic { color: var(--accent); font-size: 16px; }
.closing-contact b { color: var(--ink); font-weight: 600; }

/* ============================================================
   CONTENTS
   ============================================================ */
.section-label {
  display: flex; align-items: center; gap: 12px;
  font-family: var(--font-mono); font-size: 12px; letter-spacing: .14em;
  text-transform: uppercase; color: var(--muted); margin-bottom: 8px;
}
.section-label::after { content: ""; flex: 1; height: 1px; background: var(--line); }
.toc-h {
  font-family: var(--font-display); font-weight: 600; letter-spacing: -.025em;
  font-size: 40px; margin: 0 0 36px;
}
.phase-block { margin-bottom: 30px; }
.phase-head {
  display: flex; align-items: center; gap: 12px; margin-bottom: 12px;
}
.phase-head .badge {
  width: 34px; height: 34px; border-radius: 9px; flex: none;
  display: grid; place-items: center; color: #fff;
  background: var(--accent); font-size: 18px;
}
.phase-head .pname {
  font-family: var(--font-display); font-weight: 600; font-size: 18px;
  letter-spacing: -.01em;
}
.phase-head .prange {
  font-family: var(--font-mono); font-size: 12px; color: var(--muted);
  border: 1px solid var(--line); border-radius: 999px; padding: 3px 9px;
}
.phase-head .pline { flex: 1; height: 1px; background: var(--line-soft); }

.toc-row {
  display: grid; grid-template-columns: 54px 1fr auto;
  align-items: center; gap: 16px;
  padding: 12px 14px 12px 8px;
  border-radius: 10px; text-decoration: none; color: inherit;
  border: 1px solid transparent;
}
.toc-row:hover { background: var(--paper-2); border-color: var(--line); }
.toc-row .num {
  font-family: var(--font-display); font-weight: 600; font-size: 22px;
  color: var(--accent); text-align: center;
}
.toc-row .tt { display: flex; align-items: center; gap: 11px; min-width: 0; }
.toc-row .tt .ic {
  font-size: 20px; color: var(--accent); flex: none;
  width: 38px; height: 38px; border-radius: 9px;
  display: grid; place-items: center;
  background: color-mix(in srgb, var(--accent) 9%, transparent);
}
.toc-row .tt .label { font-weight: 500; font-size: 16px; letter-spacing: -.01em; }
.toc-row .arrow { color: var(--muted); font-size: 18px; opacity: 0; transition: .15s; }
.toc-row:hover .arrow { opacity: 1; }

/* ============================================================
   DAY
   ============================================================ */
.day-head {
  position: relative; padding: 54px 68px 30px;
  border-bottom: 1px solid var(--line);
  background:
    linear-gradient(180deg, color-mix(in srgb, var(--accent) 6%, var(--paper)), var(--paper));
}
.day-head .eyebrow {
  display: flex; align-items: center; gap: 10px; flex-wrap: wrap;
  font-family: var(--font-mono); font-size: 12px; letter-spacing: .1em;
  text-transform: uppercase; color: var(--accent); margin-bottom: 14px;
}
.day-head .eyebrow .ph {
  color: var(--ink-soft); border: 1px solid var(--line);
  border-radius: 999px; padding: 3px 9px; letter-spacing: .08em;
}
.day-head .title-row { display: flex; align-items: center; gap: 22px; }
.day-head .bignum {
  font-family: var(--font-display); font-weight: 600; line-height: .85;
  font-size: 92px; letter-spacing: -.04em;
  color: transparent; -webkit-text-stroke: 1.5px color-mix(in srgb, var(--accent) 55%, var(--line));
  flex: none;
}
.day-head .ttl {
  font-family: var(--font-display); font-weight: 600; letter-spacing: -.025em;
  font-size: 33px; line-height: 1.06; margin: 0;
}
.day-head .glyph {
  margin-left: auto; flex: none;
  width: 56px; height: 56px; border-radius: 14px;
  display: grid; place-items: center; font-size: 28px; color: #fff;
  background: var(--accent);
  box-shadow: 0 14px 30px -12px color-mix(in srgb, var(--accent) 70%, transparent);
}

.day-body { padding: 38px 68px 60px; }

/* block heading with icon */
.block-label {
  display: flex; align-items: center; gap: 11px; margin: 40px 0 18px;
}
.block-label:first-child { margin-top: 4px; }
.block-label .ico {
  width: 34px; height: 34px; border-radius: 9px; flex: none;
  display: grid; place-items: center; font-size: 18px;
  color: var(--accent);
  background: color-mix(in srgb, var(--accent) 10%, transparent);
}
.block-label .txt {
  font-family: var(--font-display); font-weight: 600; font-size: 14px;
  letter-spacing: .08em; text-transform: uppercase;
}
.block-label .meta {
  font-family: var(--font-mono); font-size: 11px; color: var(--muted);
  margin-left: auto;
}

/* objectives */
.objectives {
  list-style: none; margin: 0; padding: 18px 22px;
  background: var(--paper-2); border: 1px solid var(--line);
  border-radius: 12px; display: grid; gap: 12px;
}
.objectives li { display: flex; align-items: flex-start; gap: 12px; }
.objectives .chk {
  width: 22px; height: 22px; border-radius: 7px; flex: none; margin-top: 1px;
  display: grid; place-items: center; font-size: 13px; color: #fff;
  background: var(--accent);
}
.objectives li span { font-size: 15.5px; }

/* theory block */
.tblock { margin-top: 24px; }
.tblock h4 {
  font-family: var(--font-display); font-weight: 600; font-size: 20px;
  letter-spacing: -.015em; margin: 0 0 7px;
}
.tblock .intro { margin: 0 0 14px; color: var(--ink-soft); }
.tlist { list-style: none; margin: 0; padding: 0; display: grid; gap: 9px; }
.tlist li { display: flex; gap: 11px; align-items: flex-start; font-size: 15px; }
.tlist li::before {
  content: ""; width: 6px; height: 6px; border-radius: 2px; margin-top: 9px;
  flex: none; background: var(--accent);
  transform: rotate(45deg);
}
.tlist.ord { counter-reset: s; }
.tlist.ord li::before { display: none; }
.tlist.ord li {
  counter-increment: s;
}
.tlist.ord li .n {
  font-family: var(--font-mono); font-size: 12px; font-weight: 600;
  width: 22px; height: 22px; border-radius: 6px; flex: none; margin-top: 0;
  display: grid; place-items: center; color: var(--accent);
  background: color-mix(in srgb, var(--accent) 11%, transparent);
}

/* formula chip */
.formula {
  margin: 16px 0 0; padding: 14px 18px;
  font-family: var(--font-mono); font-size: 14.5px; color: var(--ink);
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-left: 3px solid var(--accent);
  border-radius: 8px; overflow-x: auto;
  display: flex; align-items: center; gap: 12px;
}
.formula .fx { color: var(--accent); flex: none; font-size: 16px; }
.formula code { white-space: nowrap; }

/* tip callout */
.tip {
  margin: 16px 0 0; display: flex; gap: 12px; align-items: flex-start;
  padding: 13px 16px; border-radius: 10px; font-size: 14.5px;
  color: var(--ink-soft);
  background: color-mix(in srgb, var(--accent) 7%, var(--paper));
  border: 1px solid color-mix(in srgb, var(--accent) 22%, transparent);
}
.tip .ico { color: var(--accent); font-size: 17px; flex: none; margin-top: 1px; }
.tip b { color: var(--ink); font-weight: 600; }

/* practical steps + code */
.pintro { color: var(--ink-soft); margin: 0 0 18px; }
.step { margin-top: 22px; }
.step .sh {
  font-family: var(--font-display); font-weight: 600; font-size: 16px;
  margin: 0 0 10px; display: flex; align-items: center; gap: 9px;
}
.step .sh .ic { color: var(--accent); font-size: 16px; }
.code {
  background: var(--code-bg); border-radius: 12px; overflow: hidden;
  border: 1px solid var(--code-line);
}
.code .bar {
  display: flex; align-items: center; gap: 7px;
  padding: 9px 14px; border-bottom: 1px solid var(--code-line);
}
.code .bar .d { width: 10px; height: 10px; border-radius: 50%; }
.code .bar .d.r { background: #FF5F57; }
.code .bar .d.y { background: #FEBC2E; }
.code .bar .d.g { background: #28C840; }
.code .bar .lang {
  margin-left: auto; font-family: var(--font-mono); font-size: 10.5px;
  letter-spacing: .12em; text-transform: uppercase; color: var(--code-dim);
}
.code pre {
  margin: 0; padding: 16px 18px; overflow-x: auto;
  font-family: var(--font-mono); font-size: 13px; line-height: 1.65;
  color: var(--code-fg);
  -webkit-text-size-adjust: 100%;
}
.code pre .cmt { color: #6B7180; font-style: italic; }
.code pre .kw  { color: #FF9D7A; }
.code pre .str { color: #9DE08B; }
.code pre .num { color: #E5C07B; }
.code pre .fn  { color: #82AAFF; }

/* practice tasks */
.tasks {
  margin: 4px 0 0; padding: 20px 22px; list-style: none;
  border: 1px dashed color-mix(in srgb, var(--accent) 40%, var(--line));
  border-radius: 12px;
  background: color-mix(in srgb, var(--accent) 4%, var(--paper));
  display: grid; gap: 13px;
}
.tasks li { display: flex; gap: 13px; align-items: flex-start; font-size: 15px; }
.tasks .box {
  width: 19px; height: 19px; border-radius: 5px; flex: none; margin-top: 2px;
  border: 1.5px solid color-mix(in srgb, var(--accent) 60%, var(--muted));
}

.day-foot {
  display: flex; align-items: center; justify-content: space-between;
  margin-top: 40px; padding-top: 18px; border-top: 1px solid var(--line);
  font-family: var(--font-mono); font-size: 11.5px; color: var(--muted);
}
.day-foot .clock { display: inline-flex; align-items: center; gap: 6px; }

/* closing card */
.closing { text-align: center; padding: 72px 60px; }
.closing .ic-lg { font-size: 40px; color: var(--accent); }
.closing h2 {
  font-family: var(--font-display); font-weight: 600; font-size: 34px;
  letter-spacing: -.02em; margin: 18px 0 10px;
}
.closing p { color: var(--ink-soft); max-width: 440px; margin: 0 auto; }

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 720px) {
  .doc { padding: 16px 12px 80px; }
  .page-pad, .cover { padding: 36px 24px; }
  .day-head { padding: 34px 24px 22px; }
  .day-body { padding: 28px 24px 40px; }
  .cover h1 { font-size: 52px; }
  .cover .sub { font-size: 20px; }
  .day-head .bignum { font-size: 64px; }
  .day-head .ttl { font-size: 25px; }
  .day-head .glyph { display: none; }
  .toc-h { font-size: 30px; }
  .topbar nav { display: none; }
}

/* ============================================================
   Print
   ============================================================ */
@media print {
  @page { size: A4; margin: 14mm 13mm; }
  body { background: #fff; }
  .topbar { display: none !important; }
  .doc { padding: 0; max-width: none; }
  .page {
    box-shadow: none; border: none; border-radius: 0;
    margin: 0; max-width: none;
    break-inside: avoid-page;
  }
  .page + .page, .day { break-before: page; }
  .cover { -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .code, .cover, .day-head, .objectives, .tip, .tasks, .formula,
  .phase-head .badge, .toc-row .num { -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  .block-label, .step, .tblock, .objectives, .tasks { break-inside: avoid; }
}