/* Palette defined light-first on :root, with dark redefined under
   prefers-color-scheme, so the page follows the reader's system setting
   without a toggle to build, store or get wrong. */
:root {
  --bg: #ffffff;
  --bg-alt: #f6f7f9;
  --fg: #1b1f24;
  --muted: #57606a;
  --border: #d8dee4;
  --accent: #0969da;
  --code-bg: #f2f4f7;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d1117; --bg-alt: #161b22; --fg: #e6edf3; --muted: #9198a1;
    --border: #30363d; --accent: #58a6ff; --code-bg: #161b22;
  }
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--fg);
  font-family: var(--sans); display: flex; flex-direction: column;
}

header {
  display: flex; align-items: center; justify-content: space-between; gap: 1rem;
  padding: .6rem 1rem; border-bottom: 1px solid var(--border); background: var(--bg-alt);
  flex: 0 0 auto;
}
header h1 { font-size: .95rem; font-weight: 600; margin: 0; letter-spacing: .01em; }
.actions { display: flex; gap: .5rem; }
.btn {
  font: inherit; font-size: .85rem; color: var(--fg); background: var(--bg);
  border: 1px solid var(--border); border-radius: 6px; padding: .35rem .75rem;
  cursor: pointer; line-height: 1.4;
}
.btn:hover { border-color: var(--accent); color: var(--accent); }

main { flex: 1 1 auto; display: grid; grid-template-columns: 1fr 1fr; min-height: 0; }
.pane { min-width: 0; min-height: 0; display: flex; position: relative; }
.pane + .pane { border-left: 1px solid var(--border); }

#src {
  flex: 1; width: 100%; resize: none; border: 0; outline: none;
  padding: 1.25rem 1.5rem; background: var(--bg); color: var(--fg);
  font-family: var(--mono); font-size: .875rem; line-height: 1.7; tab-size: 2;
}
.rendered { flex: 1; overflow-y: auto; padding: 1.25rem 1.75rem; line-height: 1.65; }
/* A comfortable measure. Full-width prose in a half-screen pane is unreadable. */
.rendered > * { max-width: 46rem; }

.rendered h1, .rendered h2, .rendered h3,
.rendered h4, .rendered h5, .rendered h6 { line-height: 1.25; margin: 1.6em 0 .6em; font-weight: 600; }
.rendered > :first-child { margin-top: 0; }
.rendered h1 { font-size: 1.9rem; padding-bottom: .3em; border-bottom: 1px solid var(--border); }
.rendered h2 { font-size: 1.45rem; padding-bottom: .3em; border-bottom: 1px solid var(--border); }
.rendered h3 { font-size: 1.2rem; }
.rendered p, .rendered ul, .rendered ol, .rendered blockquote, .rendered table { margin: 0 0 1em; }
.rendered a { color: var(--accent); text-decoration: none; }
.rendered a:hover { text-decoration: underline; }
.rendered strong { font-weight: 600; }
.rendered ul, .rendered ol { padding-left: 1.5em; }
.rendered li + li { margin-top: .25em; }
.rendered li input[type=checkbox] { margin-right: .4em; }

.rendered blockquote {
  margin-left: 0; padding: .1em 1em; color: var(--muted);
  border-left: .25em solid var(--border);
}
.rendered code {
  font-family: var(--mono); font-size: .85em; background: var(--code-bg);
  padding: .2em .4em; border-radius: 5px;
}
.rendered pre {
  background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 1em; overflow-x: auto; margin: 0 0 1em;
}
.rendered pre code { background: none; padding: 0; font-size: .85rem; line-height: 1.55; }
.rendered table { border-collapse: collapse; display: block; overflow-x: auto; }
.rendered th, .rendered td { border: 1px solid var(--border); padding: .45em .8em; }
.rendered th { background: var(--bg-alt); font-weight: 600; }
.rendered img { max-width: 100%; height: auto; border-radius: 6px; }
.rendered hr { border: 0; border-top: 1px solid var(--border); margin: 2em 0; }

/* Hidden by default and shown with a class, NOT with the hidden attribute.
   An author rule setting `display` on an id beats the browser's
   `[hidden] { display: none }`, so `#drop { display: grid }` left this overlay
   permanently on top of the page - it covered the whole app on every device. */
#drop {
  position: fixed; inset: 0; display: none; place-items: center;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  border: 3px dashed var(--accent); font-size: 1.1rem; color: var(--accent); z-index: 10;
}
#drop.show { display: grid; }

/* Narrow screens: stack instead of two unusable columns. */
@media (max-width: 800px) {
  main { grid-template-columns: 1fr; grid-template-rows: 1fr 1fr; }
  .pane + .pane { border-left: 0; border-top: 1px solid var(--border); }
}

/* Transient hint, used when the clipboard API is unavailable and the user has
   to press Ctrl/Cmd+V themselves. */
#note {
  position: fixed; left: 50%; bottom: 1.5rem; transform: translateX(-50%);
  background: var(--fg); color: var(--bg); padding: .5rem 1rem;
  border-radius: 6px; font-size: .85rem; z-index: 20;
}
#note[hidden] { display: none; }   /* explicit, for the same reason as #drop */

/* The right pane starts empty; without this it reads as broken rather than
   as waiting for input. */
.rendered:empty::before {
  content: "Formatted markdown appears here.";
  color: var(--muted); font-style: italic;
}

/* Touch devices have no drag-and-drop, so the overlay can never be correct
   there - belt and braces after it shipped stuck-on. */
@media (hover: none) and (pointer: coarse) {
  #drop { display: none !important; }
}

/* Full-screen toggle, one per pane. Sits over its own pane, dim until hovered
   so it does not compete with the text. */
.expand {
  position: absolute; top: .5rem; right: .5rem; z-index: 5;
  font: inherit; font-size: .9rem; line-height: 1;
  color: var(--muted); background: var(--bg); border: 1px solid var(--border);
  border-radius: 6px; padding: .3rem .45rem; cursor: pointer; opacity: .55;
}
.expand:hover, .expand:focus-visible { opacity: 1; color: var(--accent); border-color: var(--accent); }
.expand svg { display: block; transition: transform .15s ease; }
/* Rotated when that pane is expanded - the only state change the button needs,
   and it costs no font support. */
.expand[aria-pressed="true"] { opacity: 1; color: var(--accent); border-color: var(--accent); }
.expand[aria-pressed="true"] svg { transform: rotate(45deg); }

/* Both grid properties are set so this works at either breakpoint - the narrow
   layout uses rows, the wide one uses columns. Class on main outranks the
   media query by specificity, so source order does not matter. */
main.focus-src, main.focus-out { grid-template-columns: 1fr; grid-template-rows: 1fr; }
main.focus-src #pane-out, main.focus-out #pane-src { display: none; }
main.focus-src #pane-src, main.focus-out #pane-out { border: 0; }