:root {
  color-scheme: light;
  --paper: #edf3f8;
  --ink: #172c43;
  --signal: #d4663c;
  --teal: #277c7a;
  --surface: #f9fbfd;
  --muted: #4b6276;
  --rule: #c6d3df;
  --display: "Trebuchet MS", "Segoe UI", sans-serif;
  --body: "Segoe UI", system-ui, sans-serif;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; color: var(--ink); background-color: var(--paper); background-image: linear-gradient(#172c4305 1px, transparent 1px), linear-gradient(90deg, #172c4305 1px, transparent 1px); background-size: 32px 32px; font: 16px/1.6 var(--body); }
a { color: inherit; text-underline-offset: .2em; }
a:focus-visible { outline: 3px solid var(--teal); outline-offset: 5px; }
[hidden] { display: none !important; }
::selection { background: #b8d8d6; color: var(--ink); }
.page-shell { width: min(1160px, calc(100% - 80px)); margin-inline: auto; }
.skip-link { position: fixed; z-index: 10; top: 12px; left: 12px; padding: 12px 20px; color: var(--surface); background: var(--ink); transform: translateY(-160%); }
.skip-link:focus { transform: translateY(0); }
.masthead { min-height: 116px; display: flex; align-items: center; justify-content: space-between; gap: 24px; border-bottom: 1px solid var(--rule); }
.wordmark { display: inline-flex; gap: 12px; align-items: center; text-decoration: none; font: 700 32px/1 var(--display); letter-spacing: -.06em; }
.wordmark svg { width: 30px; height: 30px; }
.wordmark-dot { color: var(--signal); }
.owner { margin: 0; font-size: 13px; line-height: 1.7; text-align: right; }
.owner span { display: block; color: var(--muted); font-size: 12px; }
.intro { display: grid; grid-template-columns: 1.3fr 1fr; align-items: end; gap: 60px; padding-block: 70px 62px; }
.eyebrow { margin: 0 0 22px; text-transform: uppercase; font-size: 11px; font-weight: 650; letter-spacing: .16em; }
h1 { margin: 0; max-width: 740px; font: 700 clamp(48px, 5.8vw, 76px)/1.02 var(--display); letter-spacing: -.055em; }
.accent { color: var(--signal); }
.intro-copy { margin: 0 0 4px; padding-left: 24px; border-left: 2px solid var(--teal); font-size: 17px; line-height: 1.7; color: var(--muted); }
.section-heading { display: flex; justify-content: space-between; align-items: baseline; gap: 20px; margin-bottom: 17px; }
.section-heading h2, .study-method > h2 { margin: 0; font-size: 12px; font-weight: 650; letter-spacing: .08em; text-transform: uppercase; }
.section-heading > span { color: var(--muted); font-size: 12px; }
.course { display: grid; grid-template-columns: .95fr 1.05fr; border: 1px solid #b7c8d6; background: var(--surface); box-shadow: 7px 8px 0 #dce6ee; }
.diagram-panel { margin: 0; display: flex; flex-direction: column; justify-content: center; border-right: 1px solid #b7c8d6; background: #e4edf5; overflow: hidden; }
.projection { display: block; width: 100%; height: auto; overflow: visible; }
.diagram-labels { font: italic 25px Georgia, serif; fill: var(--ink); }
.diagram-labels .coordinate { font: 17px var(--body); }
.diagram-labels .v-label { fill: #ae4925; }
.diagram-labels .p-label { fill: #206968; }
.diagram-labels .origin-label { font: 15px var(--body); }
.diagram-labels .span-label { font-size: 19px; fill: #206968; }
.diagram-labels .axis-note { font: 15px var(--body); fill: var(--muted); }
.diagram-panel figcaption { margin: 0 30px; padding: 18px 0 20px; border-top: 1px solid #b7c8d6; display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 10px; color: var(--muted); font-size: 11px; }
.formula { color: var(--ink); font: italic 17px Georgia, serif; white-space: nowrap; }
.formula > span { padding-inline: 7px; font-style: normal; }
.course-content { display: flex; flex-direction: column; align-items: flex-start; padding: 41px 42px 38px; }
.course-field { margin: 0 0 15px; color: var(--teal); font-size: 11px; line-height: 1.5; letter-spacing: .1em; font-weight: 650; text-transform: uppercase; }
.course-content h3 { margin: 0 0 21px; font: 700 clamp(36px, 4.15vw, 52px)/1.03 var(--display); letter-spacing: -.045em; }
.course-description { max-width: 410px; margin: 0 0 20px; font-size: 14px; line-height: 1.75; color: var(--muted); }
.course-meta { display: flex; flex-wrap: wrap; list-style: none; margin: 0 0 31px; padding: 0; gap: 8px 13px; font-size: 11px; font-weight: 600; }
.course-meta li + li::before { content: "·"; padding-right: 13px; color: #7891a5; }
.course-actions { margin-top: auto; display: flex; align-items: center; flex-wrap: wrap; gap: 13px 20px; width: 100%; }
.button { min-height: 48px; display: inline-flex; align-items: center; justify-content: space-between; gap: 24px; padding: 12px 19px; text-decoration: none; font-size: 13px; font-weight: 600; line-height: 1.5; border: 1px solid transparent; transition: background-color .18s, border-color .18s, color .18s; }
.button-primary { color: var(--surface); background: var(--ink); }
.button-primary:hover { background: var(--teal); }
.button-primary span { font-size: 20px; font-weight: 400; line-height: 1; }
.button-secondary { padding-inline: 0; color: var(--ink); background: transparent; border-radius: 0; }
.button-secondary:hover { color: var(--teal); text-decoration: underline; }
.button-secondary span { font-size: 17px; }
.course-progress { width: 100%; margin-top: -5px; margin-bottom: 24px; }
.progress-label { display: flex; align-items: baseline; justify-content: space-between; gap: 10px; font-size: 11px; font-weight: 600; }
.course-progress progress { display: block; appearance: none; width: 100%; height: 4px; margin-top: 8px; border: 0; background: #dce6ee; color: var(--teal); }
.course-progress progress::-webkit-progress-bar { background: #dce6ee; }
.course-progress progress::-webkit-progress-value { background: var(--teal); }
.course-progress progress::-moz-progress-bar { background: var(--teal); }
.local-note { margin: 6px 0 0; font-size: 10px; color: var(--muted); }
.study-method { padding-block: 65px 58px; }
.study-method > h2 { margin-bottom: 27px; }
.study-steps { display: grid; grid-template-columns: repeat(3, 1fr); gap: 40px; }
.study-step { display: grid; grid-template-columns: 28px 1fr; align-items: baseline; column-gap: 12px; }
.step-mark { grid-row: 1 / 3; font: 400 25px/1 Georgia, serif; color: var(--teal); }
.step-work { color: #ae4925; }
.step-review { color: var(--ink); }
.study-step h3 { margin: 0 0 9px; font: 700 19px/1.3 var(--display); letter-spacing: -.02em; }
.study-step p { margin: 0; font-size: 12px; line-height: 1.8; color: var(--muted); }
.footer { display: flex; align-items: baseline; justify-content: space-between; gap: 25px; padding-block: 22px 28px; border-top: 1px solid var(--rule); color: var(--muted); font-size: 10px; }
.footer > span { color: var(--ink); }
.footer p { max-width: 430px; margin: 0; text-align: right; }
@keyframes vector-in { from { stroke-dashoffset: 1; opacity: 0; } to { stroke-dashoffset: 0; opacity: 1; } }
@keyframes ink-in { from { opacity: 0; } to { opacity: 1; } }
.vector { stroke-dasharray: 1; animation: vector-in 1.1s cubic-bezier(.22,.68,.2,1) both; }
.vector-projection { animation-delay: .2s; }
.vector-original { animation-delay: .45s; }
.residual, .right-angle, .diagram-labels { animation: ink-in .7s .9s both; }
@media (min-width: 1440px) { .intro { padding-top: 85px; } }
@media (max-width: 1000px) {
  .page-shell { width: calc(100% - 64px); }
  .intro { gap: 35px; }
  .intro-copy { font-size: 15px; }
  .course-content { padding: 30px; }
  .course-meta { gap: 6px 10px; }
  .course-meta li + li::before { padding-right: 10px; }
  .diagram-panel figcaption { margin-inline: 22px; }
  .study-steps { gap: 24px; }
}
@media (max-width: 760px) {
  .page-shell { width: calc(100% - 40px); }
  .masthead { min-height: 88px; }
  .wordmark { font-size: 29px; gap: 8px; }
  .wordmark svg { width: 25px; height: 25px; }
  .owner { font-size: 11px; }
  .owner span { font-size: 10px; }
  .intro { grid-template-columns: 1fr; gap: 27px; padding-block: 43px 40px; }
  .eyebrow { margin-bottom: 18px; font-size: 10px; }
  h1 { font-size: clamp(44px, 9vw, 64px); }
  .intro-copy { margin: 0; padding-left: 15px; font-size: 14px; }
  .desktop-break { display: none; }
  .section-heading { gap: 12px; margin-bottom: 13px; }
  .section-heading h2 { font-size: 10px; }
  .section-heading > span { font-size: 10px; }
  .course { grid-template-columns: 1fr; box-shadow: 5px 6px 0 #dce6ee; }
  .diagram-panel { border-right: 0; border-bottom: 1px solid #b7c8d6; }
  .projection { max-height: 310px; }
  .diagram-panel figcaption { padding-block: 13px; font-size: 10px; }
  .formula { font-size: 15px; }
  .course-content { padding: 28px 26px; }
  .course-field { font-size: 10px; margin-bottom: 13px; }
  .course-content h3 { font-size: 43px; margin-bottom: 18px; }
  .course-description { font-size: 13px; max-width: 100%; }
  .course-meta { margin-bottom: 25px; font-size: 10px; }
  .course-actions { gap: 8px 18px; }
  .study-method { padding-block: 43px 35px; }
  .study-method > h2 { margin-bottom: 25px; font-size: 10px; }
  .study-steps { grid-template-columns: 1fr; gap: 25px; }
  .study-step { grid-template-columns: 25px 1fr; column-gap: 13px; }
  .study-step h3 { margin-bottom: 5px; font-size: 18px; }
  .study-step p { max-width: 450px; font-size: 12px; }
  .footer { display: block; padding-bottom: 25px; }
  .footer p { margin-top: 6px; text-align: left; max-width: 300px; }
}
@media (max-width: 360px) {
  .page-shell { width: calc(100% - 30px); }
  h1 { font-size: 41px; }
  .course-content { padding-inline: 21px; }
  .section-heading > span { font-size: 9px; }
  .diagram-panel figcaption { margin-inline: 18px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
  .vector { stroke-dashoffset: 0; }
}