/* Measured from highagency.com 2026-10-08, viewport 1440.
   Body computed Poppins 16/28 is the page chrome. Article paragraphs compute
   Mpro, Georgia, sans-serif 22px / 36.3px. Headings compute Poppins 500.
   Korean stand-in: Pretendard (grotesk) for Poppins, and for the body because
   a Georgia serif breaks Hangul. Measure column 800px. White ground, black ink.
   User override: clone this site, do not restyle as the openai learning doc. */
@font-face {
  font-family: "Pretendard";
  font-weight: 400;
  font-style: normal;
  font-display: swap;
  src: url("https://cdn.jsdelivr.net/gh/orioncactus/pretendard@v1.3.9/dist/web/static/woff2/Pretendard-Regular.woff2") format("woff2");
}
@font-face {
  font-family: "Pretendard";
  font-weight: 500;
  font-style: normal;
  font-display: swap;
  src: url("https://cdn.jsdelivr.net/gh/orioncactus/pretendard@v1.3.9/dist/web/static/woff2/Pretendard-Medium.woff2") format("woff2");
}
@font-face {
  font-family: "Pretendard";
  font-weight: 600;
  font-style: normal;
  font-display: swap;
  src: url("https://cdn.jsdelivr.net/gh/orioncactus/pretendard@v1.3.9/dist/web/static/woff2/Pretendard-SemiBold.woff2") format("woff2");
}
:root {
  --ink: #000;
  --paper: #fff;
  --muted: #515151;
  --hair: #e6e6e6;
  --chip: #f7f7f7;
  --measure: 800px;
  --sans: "Pretendard", "Poppins", -apple-system, BlinkMacSystemFont, sans-serif;
  --invert-ink: #fff;
  color-scheme: light;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  font-weight: 400;
  line-height: 28px;
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; }
img { max-width: 100%; height: auto; display: block; }
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: 1140px;
  margin: 0 auto;
  padding: 22px 40px 0;
}
.brand {
  font-weight: 500;
  font-size: 22px;
  letter-spacing: -0.3px;
  text-decoration: none;
}
.brand small { font-weight: 400; color: var(--muted); font-size: 13px; margin-left: 8px; }
.hero {
  max-width: 1140px;
  margin: 0 auto;
  padding: 72px 40px 24px;
}
.hero h1 {
  font-family: var(--sans);
  font-weight: 500;
  font-size: 60px;
  line-height: 75px;
  letter-spacing: -0.5px;
  margin: 0 0 8px;
}
.hero .sub {
  font-size: 22px;
  line-height: 36px;
  color: var(--muted);
  margin: 0 0 18px;
}
.byline { font-size: 16px; color: var(--ink); margin: 0; }
.layout {
  max-width: 1140px;
  margin: 0 auto;
  padding: 10px 40px 80px;
  display: grid;
  grid-template-columns: 240px minmax(0, var(--measure));
  gap: 40px;
  justify-content: center;
}
nav.contents {
  position: sticky;
  top: 24px;
  align-self: start;
  max-height: calc(100vh - 48px);
  overflow: auto;
  font-size: 13px;
  line-height: 1.45;
  padding-right: 8px;
  scrollbar-width: thin;
}
nav.contents .label {
  font-size: 12px;
  letter-spacing: 0.08em;
  color: var(--muted);
  margin: 0 0 10px;
}
nav.contents a {
  display: block;
  text-decoration: none;
  color: #333;
  padding: 4px 0;
}
nav.contents a.part { font-weight: 600; margin-top: 10px; color: #000; }
nav.contents a:hover { text-decoration: underline; }
article.essay {
  max-width: var(--measure);
  font-size: 22px;
  line-height: 36.3px;
  font-weight: 400;
}
article.essay h2 {
  font-weight: 500;
  font-size: 36px;
  line-height: 1.25;
  letter-spacing: -0.4px;
  margin: 64px 0 18px;
}
article.essay h3 {
  font-weight: 500;
  font-size: 27px;
  line-height: 1.3;
  margin: 40px 0 12px;
}
article.essay h4 {
  font-weight: 500;
  font-size: 24px;
  line-height: 1.35;
  margin: 28px 0 10px;
}
article.essay p { margin: 0 0 18px; }
article.essay ul, article.essay ol { margin: 0 0 18px; padding-left: 1.2em; }
article.essay li { margin: 0 0 8px; }
article.essay blockquote {
  margin: 8px 0 22px;
  padding: 4px 0 4px 18px;
  border-left: 2px solid #000;
}
article.essay blockquote p { margin: 0 0 8px; }
article.essay cite { display: block; font-style: normal; font-size: 16px; line-height: 24px; color: var(--muted); }
article.essay .via { font-size: 16px; line-height: 24px; color: var(--muted); }
figure.fig { margin: 18px 0 28px; }
figure.fig img { width: 100%; height: auto; background: var(--chip); }
figure.fig figcaption, p.cap {
  font-size: 14px;
  line-height: 20px;
  color: var(--muted);
  margin-top: 8px;
}
.yt {
  position: relative;
  margin: 18px 0 28px;
  background: #000;
  aspect-ratio: 16 / 9;
  cursor: pointer;
}
.yt img { width: 100%; height: 100%; object-fit: cover; opacity: 0.92; }
.yt button {
  position: absolute;
  inset: 0;
  margin: auto;
  width: 68px;
  height: 48px;
  border: 0;
  background: #ff0000;
  color: #fff;
  font-size: 18px;
  cursor: pointer;
}
.yt iframe { width: 100%; height: 100%; border: 0; position: absolute; inset: 0; }
form.signup {
  margin: 28px 0;
  padding: 22px;
  background: #f7f7f7;
  display: grid;
  gap: 10px;
}
form.signup p { font-size: 18px; line-height: 28px; margin: 0; }
form.signup input[type="email"] {
  font: inherit;
  font-size: 16px;
  padding: 12px 14px;
  border: 1px solid #000;
  background: #fff;
  color: #000;
  border-radius: 0;
  width: 100%;
}
form.signup button {
  font: inherit;
  font-size: 16px;
  font-weight: 500;
  background: #000;
  color: #fff;
  border: 0;
  padding: 12px 18px;
  cursor: pointer;
  justify-self: start;
}
.share { display: flex; flex-wrap: wrap; gap: 14px 18px; margin: 12px 0 28px; font-size: 16px; }
.share a { text-underline-offset: 3px; }
footer.colophon {
  max-width: 1140px;
  margin: 0 auto;
  padding: 10px 40px 64px;
  color: var(--muted);
  font-size: 13px;
  line-height: 20px;
}
/* link preview — contract kept, restyled to the page (square, black, no shadow) */
a.link-preview { color: inherit; text-decoration: underline; text-underline-offset: 0.18em; text-decoration-thickness: 1px; position: relative; cursor: pointer; }
a.link-preview:focus-visible { outline: 2px solid #000; outline-offset: 2px; }
a.link-preview::after {
  content: attr(data-link-type) "\A" attr(data-link-summary);
  white-space: pre-line;
  position: absolute;
  left: 0;
  bottom: calc(100% + 8px);
  z-index: 50;
  min-width: 220px;
  max-width: min(360px, 80vw);
  padding: 10px 12px;
  border-radius: 0;
  background: #000;
  color: #fff;
  font-size: 13px;
  line-height: 1.45;
  font-weight: 400;
  font-family: var(--sans);
  text-decoration: none;
  box-shadow: none;
  opacity: 0;
  pointer-events: none;
}
a.link-preview:hover::after, a.link-preview:focus::after, a.link-preview:focus-visible::after { opacity: 1; }
a.link-preview:not(:hover):not(:focus):not(:focus-visible)::after { display: none; }
@media (max-width: 900px) {
  .hero h1 { font-size: 40px; line-height: 48px; }
  .layout { grid-template-columns: 1fr; padding: 10px 20px 64px; }
  .hero, .topbar, footer.colophon { padding-left: 20px; padding-right: 20px; }
  nav.contents { position: static; max-height: none; border-bottom: 1px solid var(--hair); padding-bottom: 16px; margin-bottom: 8px; }
  article.essay { font-size: 18px; line-height: 30px; }
}