:root {
  --bg: #f4f6f8;
  --card: #ffffff;
  --ink: #1e2233;
  --muted: #5a6478;
  --line: #dde3ea;
  --brand: #1766c9;
  --brand-ink: #ffffff;
  --ok: #17864a;
  --ok-bg: #e8f6ee;
  --err: #c1372c;
  --err-bg: #fbecea;
  --shadow: 0 6px 24px rgba(20, 40, 80, .10);
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0f141b;
    --card: #171d26;
    --ink: #e7ecf3;
    --muted: #9aa6b6;
    --line: #29323f;
    --brand: #3f8ae0;
    --brand-ink: #ffffff;
    --ok: #4cc98a;
    --ok-bg: #12301f;
    --err: #f0857a;
    --err-bg: #351815;
    --shadow: 0 6px 24px rgba(0, 0, 0, .35);
  }
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Apple SD Gothic Neo", "Malgun Gothic", "Noto Sans KR", sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.6;
  min-height: 100vh;
}

header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: 720px;
  margin: 0 auto;
  padding: 18px 20px;
}
.brand {
  font-weight: 700;
  font-size: 1.15rem;
  letter-spacing: -.01em;
}
.brand .dot { color: var(--brand); }
nav.lang { display: flex; gap: 2px; font-size: .85rem; }
nav.lang a {
  text-decoration: none;
  color: var(--muted);
  padding: 4px 9px;
  border-radius: 6px;
}
nav.lang a.active { color: var(--brand); font-weight: 700; }
nav.lang a:not(.active):hover { background: var(--line); }

main {
  max-width: 720px;
  margin: 0 auto;
  padding: 8px 20px 48px;
}
.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  box-shadow: var(--shadow);
  padding: 30px 26px;
}
h1 { font-size: 1.5rem; margin: 0 0 6px; letter-spacing: -.02em; }
.lead { color: var(--muted); margin: 0 0 22px; }

.dropzone {
  border: 2px dashed var(--line);
  border-radius: 12px;
  padding: 34px 20px;
  text-align: center;
  transition: border-color .18s, background .18s;
}
.dropzone.drag { border-color: var(--brand); background: color-mix(in srgb, var(--brand) 7%, transparent); }
.btn-primary {
  appearance: none;
  border: 0;
  background: var(--brand);
  color: var(--brand-ink);
  font-size: 1rem;
  font-weight: 600;
  padding: 13px 22px;
  border-radius: 10px;
  cursor: pointer;
  transition: filter .15s, transform .02s;
}
.btn-primary:hover { filter: brightness(1.06); }
.btn-primary:active { transform: translateY(1px); }
.btn-primary:disabled { opacity: .6; cursor: default; }
.hint { color: var(--muted); font-size: .85rem; margin: 12px 0 0; }

.status, .result { margin-top: 20px; }
.spinner {
  display: inline-block;
  width: 18px; height: 18px;
  border: 2px solid var(--line);
  border-top-color: var(--brand);
  border-radius: 50%;
  animation: spin .8s linear infinite;
  vertical-align: -3px;
  margin-right: 8px;
}
@keyframes spin { to { transform: rotate(360deg); } }

.box {
  border-radius: 10px;
  padding: 16px 18px;
  font-size: .95rem;
}
.box.ok  { background: var(--ok-bg);  border: 1px solid color-mix(in srgb, var(--ok) 35%, transparent); color: var(--ok); }
.box.err { background: var(--err-bg); border: 1px solid color-mix(in srgb, var(--err) 35%, transparent); color: var(--err); }
.box .fname { font-weight: 600; word-break: break-all; }
.btn-download {
  display: inline-block;
  margin-top: 12px;
  background: var(--ok);
  color: #fff;
  text-decoration: none;
  font-weight: 600;
  padding: 10px 18px;
  border-radius: 9px;
}
.btn-download:hover { filter: brightness(1.06); }

.notice {
  margin: 22px 0 0;
  font-size: .85rem;
  color: var(--ink);
  background: color-mix(in srgb, var(--brand) 8%, transparent);
  border: 1px solid color-mix(in srgb, var(--brand) 25%, transparent);
  border-radius: 9px;
  padding: 10px 14px;
  text-align: center;
}
.privacy {
  margin: 12px 0 0;
  font-size: .85rem;
  color: var(--muted);
  text-align: center;
}
.about-link {
  margin: 18px 0 0;
  text-align: center;
}
.about-link a {
  color: var(--brand);
  text-decoration: none;
  font-weight: 600;
  font-size: .92rem;
}
.about-link a:hover { text-decoration: underline; }

/* ── about(설명) 페이지 ── */
.doc h1 { font-size: 1.55rem; margin: 0 0 4px; }
.doc .sub { color: var(--muted); margin: 0 0 24px; }
.doc h2 {
  font-size: 1.15rem;
  margin: 28px 0 8px;
  padding-top: 18px;
  border-top: 1px solid var(--line);
}
.doc h2:first-of-type { border-top: 0; padding-top: 0; }
.doc h3 { font-size: 1rem; margin: 18px 0 6px; color: var(--brand); }
.doc p { margin: 8px 0; }
.doc ul { margin: 8px 0; padding-left: 20px; }
.doc li { margin: 5px 0; }
.doc pre {
  background: color-mix(in srgb, var(--ink) 5%, var(--card));
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  overflow-x: auto;
  font-size: .78rem;
  line-height: 1.5;
}
.doc code { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; }
.callout {
  background: color-mix(in srgb, var(--brand) 7%, transparent);
  border-left: 3px solid var(--brand);
  border-radius: 6px;
  padding: 10px 14px;
  margin: 12px 0;
  font-size: .92rem;
}
.callout.warn {
  background: var(--err-bg);
  border-left-color: var(--err);
}
.back-link { margin-top: 28px; font-size: .9rem; }
.back-link a { color: var(--brand); text-decoration: none; }
.back-link a:hover { text-decoration: underline; }

/* 2겹 방어 다이어그램 */
.diagram { margin: 16px 0 4px; }
.diagram svg { width: 100%; height: auto; display: block; }
.about { margin-top: 20px; font-size: .9rem; color: var(--muted); }
.about summary { cursor: pointer; color: var(--ink); font-weight: 600; }
.about ul { margin: 10px 0 0; padding-left: 20px; }
.about li { margin: 4px 0; }

footer {
  text-align: center;
  color: var(--muted);
  font-size: .8rem;
  padding: 24px 20px 40px;
}
footer a { color: var(--muted); }