:root {
  /* Light theme — the default */
  --bg: #f1f5f9;
  --panel: #ffffff;
  --panel-2: #edf1f6;
  --border: #d6dee8;
  --text: #0f172a;
  --muted: #586472;
  --accent: #0284c7;
  --accent-strong: #075985;
  --btn-text: #ffffff;
  --link: #0369a1;
  --green: #22c55e;
  --blue: #3b82f6;
  --amber: #f59e0b;
  --red: #ef4444;
  --gray: #64748b;
  --page-bg: radial-gradient(1200px 600px at 50% -10%, #e4f0fb 0%, #f6f9fc 60%);
  --radius: 10px;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
}

/* Dark theme — opt-in via the toggle (persisted in localStorage) */
html[data-theme="dark"] {
  color-scheme: dark;
  --bg: #0f172a;
  --panel: #1e293b;
  --panel-2: #273449;
  --border: #334155;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-strong: #0ea5e9;
  --btn-text: #04121d;
  --link: #7dd3fc;
  --page-bg: radial-gradient(1200px 600px at 50% -10%, #16233d 0%, #0f172a 60%);
}

* { box-sizing: border-box; }

html { color-scheme: light; }

body {
  margin: 0;
  overflow-wrap: break-word;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--page-bg);
  color: var(--text);
  line-height: 1.5;
  min-height: 100vh;
}

.container {
  max-width: 880px;
  margin: 0 auto;
  padding: 2.5rem 1.25rem 4rem;
}

.page-header h1 {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.3rem 0.55rem;
  margin: 0 0 0.25rem;
  /* Scales down on narrow screens so the title never forces a sideways scroll. */
  font-size: clamp(1.5rem, 1.1rem + 2.2vw, 2rem);
  line-height: 1.2;
  letter-spacing: -0.02em;
}

.h1-sub {
  font-size: 0.85rem;
  font-weight: 500;
  letter-spacing: 0;
  color: var(--muted);
  flex-basis: 100%;
}

.brand-icon {
  width: 1.6em;
  height: 1.6em;
  flex: none;
}

.tagline {
  margin: 0 0 1.75rem;
  color: var(--muted);
}

.header-row {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
}

.theme-toggle {
  flex: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.4rem;
  height: 2.4rem;
  padding: 0;
  color: var(--muted);
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
}
.theme-toggle:hover {
  color: var(--text);
  border-color: var(--accent);
}
.theme-toggle:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}
.theme-toggle svg {
  width: 1.2rem;
  height: 1.2rem;
  display: block;
}
.theme-toggle .icon-sun { display: none; }
html[data-theme="dark"] .theme-toggle .icon-sun { display: block; }
html[data-theme="dark"] .theme-toggle .icon-moon { display: none; }

/* Form */
.trace-form {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
}

.input-row {
  display: flex;
  gap: 0.6rem;
}

#url-input {
  flex: 1 1 auto;
  min-width: 0;
  padding: 0.7rem 0.85rem;
  font-size: 1rem;
  color: var(--text);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  font-family: var(--mono);
}

#url-input:focus {
  outline: 2px solid var(--accent);
  outline-offset: 1px;
  border-color: var(--accent);
}

#submit-btn {
  flex: 0 0 auto;
  padding: 0.7rem 1.4rem;
  font-size: 1rem;
  font-weight: 600;
  color: var(--btn-text);
  background: var(--accent);
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

#submit-btn:hover { background: var(--accent-strong); }
#submit-btn:disabled { opacity: 0.6; cursor: progress; }

.form-controls {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  margin-top: 0.85rem;
}

.checkbox {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  cursor: pointer;
  user-select: none;
}

.checkbox input { width: 1.05rem; height: 1.05rem; accent-color: var(--accent); }

.hint { color: var(--muted); font-size: 0.85rem; }
.hint code, code { font-family: var(--mono); font-size: 0.85em; }

/* Status / error */
.status {
  min-height: 1.25rem;
  margin: 1rem 0 0;
  color: var(--muted);
}

.error {
  margin: 1.25rem 0 0;
  padding: 0.9rem 1rem;
  background: color-mix(in srgb, var(--red) 13%, var(--panel));
  border: 1px solid color-mix(in srgb, var(--red) 42%, var(--panel));
  border-radius: var(--radius);
  color: color-mix(in srgb, var(--red) 58%, var(--text));
}

.error strong { color: var(--text); }

/* Results */
.results { margin-top: 0.5rem; }

.summary {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem 1.5rem;
  align-items: center;
  padding: 1rem 1.15rem;
  margin-bottom: 1rem;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}

.summary .summary-item { display: flex; flex-direction: column; }
.summary .summary-item.full { flex: 1 1 100%; }
.summary .summary-item .label {
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--muted);
}
.summary .summary-item .value { font-weight: 600; }
.summary .final-url { font-family: var(--mono); word-break: break-all; }

.notice {
  padding: 0.8rem 1rem;
  margin-bottom: 1rem;
  border-radius: var(--radius);
  background: color-mix(in srgb, var(--amber) 14%, var(--panel));
  border: 1px solid color-mix(in srgb, var(--amber) 45%, var(--panel));
  color: color-mix(in srgb, var(--amber) 60%, var(--text));
}

/* Flag chips */
.flags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 1rem;
}
.chip {
  display: inline-block;
  padding: 0.2rem 0.7rem;
  border-radius: 999px;
  font-size: 0.8rem;
  font-weight: 600;
  border: 1px solid transparent;
}
.chip.info { background: color-mix(in srgb, var(--accent) 14%, var(--panel)); border-color: color-mix(in srgb, var(--accent) 45%, var(--panel)); color: color-mix(in srgb, var(--accent) 60%, var(--text)); }
.chip.warn { background: color-mix(in srgb, var(--amber) 14%, var(--panel)); border-color: color-mix(in srgb, var(--amber) 45%, var(--panel)); color: color-mix(in srgb, var(--amber) 60%, var(--text)); }
.chip.danger { background: color-mix(in srgb, var(--red) 14%, var(--panel)); border-color: color-mix(in srgb, var(--red) 45%, var(--panel)); color: color-mix(in srgb, var(--red) 60%, var(--text)); }

/* Redirect-type tag */
.tag {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.1rem 0.45rem;
  border-radius: 6px;
  font-weight: 700;
}
.tag.permanent { background: color-mix(in srgb, var(--blue) 16%, var(--panel)); color: color-mix(in srgb, var(--blue) 62%, var(--text)); }
.tag.temporary { background: color-mix(in srgb, var(--gray) 18%, var(--panel)); color: color-mix(in srgb, var(--gray) 68%, var(--text)); }

/* Hop list */
.hops { list-style: none; margin: 0; padding: 0; }

.hop {
  position: relative;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.9rem 1.1rem;
  margin-bottom: 0.85rem;
}

.hop-head {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 0.6rem;
}

.hop-index {
  font-family: var(--mono);
  color: var(--muted);
  font-size: 0.85rem;
}

.badge {
  display: inline-block;
  padding: 0.12rem 0.55rem;
  border-radius: 999px;
  font-family: var(--mono);
  font-weight: 700;
  font-size: 0.85rem;
  color: #04121d;
  white-space: nowrap;
}
.badge.s2 { background: var(--green); }
.badge.s3 { background: var(--blue); color: #f8fafc; }
.badge.s4 { background: var(--amber); }
.badge.s5 { background: var(--red); color: #fff; }
.badge.s0, .badge.sx { background: var(--gray); color: #f8fafc; }

.method {
  font-family: var(--mono);
  font-size: 0.8rem;
  color: var(--muted);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 0.05rem 0.4rem;
}

.hop-url {
  font-family: var(--mono);
  word-break: break-all;
  margin: 0.5rem 0 0;
  font-size: 0.92rem;
}

.hop-arrow {
  margin-top: 0.55rem;
  color: var(--muted);
  font-size: 0.9rem;
}
.hop-arrow .to {
  font-family: var(--mono);
  color: var(--link);
  word-break: break-all;
}

.timing { color: var(--muted); font-size: 0.8rem; font-family: var(--mono); }

/* Headers table */
.headers {
  margin-top: 0.7rem;
  border-top: 1px dashed var(--border);
  padding-top: 0.7rem;
}
.headers summary {
  cursor: pointer;
  color: var(--muted);
  font-size: 0.85rem;
}
.header-section { margin-top: 0.6rem; }
.header-caption {
  margin: 0 0 0.2rem;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--muted);
}
.headers table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 0.25rem;
  font-family: var(--mono);
  font-size: 0.82rem;
}
.headers th,
.headers td {
  padding: 0.25rem 0.5rem;
  vertical-align: top;
  border-bottom: 1px solid var(--panel-2);
  word-break: break-all;
}
.headers th.k {
  color: var(--link);
  white-space: nowrap;
  width: 1%;
  text-align: left;
  font-weight: 600;
}
.headers td.v { color: var(--text); }
.headers .empty { color: var(--muted); font-style: italic; }

/* Footer */
.page-footer {
  margin-top: 2.5rem;
  color: var(--muted);
  font-size: 0.85rem;
}

.visually-hidden {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

/* Skip link — first thing a keyboard user reaches, hidden until focused. */
.skip-link {
  position: absolute;
  left: 0.75rem;
  top: -3rem;
  z-index: 10;
  padding: 0.6rem 1rem;
  background: var(--panel);
  color: var(--link);
  border: 1px solid var(--accent);
  border-radius: 8px;
  text-decoration: none;
  transition: top 0.12s ease-in-out;
}
.skip-link:focus { top: 0.75rem; }

/* Explanatory copy below the tool */
.prose {
  margin-top: 3rem;
}
.prose h2 {
  margin: 2rem 0 0.6rem;
  font-size: 1.25rem;
  letter-spacing: -0.01em;
}
.prose h3 {
  margin: 1.5rem 0 0.35rem;
  font-size: 1rem;
}
.prose p { margin: 0 0 0.9rem; color: var(--muted); }
.prose strong { color: var(--text); }

.codes {
  margin: 0;
  display: grid;
  grid-template-columns: minmax(9rem, auto) 1fr;
  gap: 0.35rem 1.25rem;
  align-items: baseline;
}
.codes dt {
  font-family: var(--mono);
  font-size: 0.85rem;
  font-weight: 700;
}
.codes dd {
  margin: 0;
  color: var(--muted);
}

/* Visible focus for every interactive element, not just the ones with custom styles. */
#submit-btn:focus-visible,
.checkbox input:focus-visible,
.headers summary:focus-visible,
.skip-link:focus-visible,
a:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; animation: none !important; }
}

@media (max-width: 700px) {
  .container { padding: 1.75rem 1rem 3rem; }
  .prose { margin-top: 2.25rem; }
  .codes { grid-template-columns: 1fr; gap: 0.15rem; }
  .codes dd { margin-bottom: 0.5rem; }
}

@media (max-width: 560px) {
  /* Let long header names wrap rather than widening the table past the viewport.
     The table keeps its markup — no display:block, which would strip the row/column
     semantics screen readers rely on. */
  .headers th.k { white-space: normal; width: 32%; }
  .summary { padding: 0.9rem 1rem; gap: 0.7rem 1.25rem; }
  /* Comfortable touch target on phones. */
  .theme-toggle { width: 2.75rem; height: 2.75rem; }
}

@media (max-width: 520px) {
  .input-row { flex-direction: column; }
  #submit-btn { width: 100%; }
  .form-controls { flex-direction: column; align-items: flex-start; gap: 0.4rem; }
}