*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg: #0d1117;
  --surface: #161b22;
  --border: #30363d;
  --text: #abb2bf;
  --text-muted: #8b949e;
  --btn-bg: #21262d;
  --btn-hover: #30363d;
  --radius: 6px;
  --header-h: 56px;
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  --font-size: 0.8rem;
  --line-height: 1.6;
  --pad: 0.75rem;
}

body {
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-size: 14px;
  height: 100vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

/* ── Header ── */
header {
  height: var(--header-h);
  padding: 0 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-shrink: 0;
  gap: 1rem;
}

.header-left h1 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text);
  letter-spacing: 0.02em;
  line-height: 1.2;
}

.header-left p {
  color: var(--text-muted);
  font-size: 0.75rem;
  margin-top: 0.1rem;
}

/* ── Star button ── */
.star-btn {
  display: inline-flex;
  align-items: stretch;
  text-decoration: none;
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  white-space: nowrap;
  transition: border-color 0.15s;
  line-height: 1;
}

.star-btn:hover {
  border-color: #8b949e;
}

/* Left part: GitHub icon + star icon + "Star" text */
.star-btn-icon,
.star-btn-star {
  flex-shrink: 0;
}

.star-btn-icon {
  width: 14px;
  height: 14px;
  fill: var(--text-muted);
  align-self: center;
  margin-left: 8px;
}

.star-btn-star {
  width: 12px;
  height: 12px;
  fill: #e3b341;
  align-self: center;
  margin: 0 5px 0 6px;
}

.star-btn-divider {
  display: inline-block;
  width: 1px;
  align-self: stretch;
  background: var(--border);
  margin: 0 0 0 8px;
  flex-shrink: 0;
}

.star-btn-count {
  padding: 0 8px;
  display: inline-flex;
  align-items: center;
  background: var(--btn-bg);
  color: var(--text);
  font-size: 0.75rem;
  font-weight: 600;
  transition: background 0.15s;
}

.star-btn:hover .star-btn-count {
  background: var(--btn-hover);
}

/* ── Main layout ── */
main {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  padding: 1rem;
  flex: 1;
  min-height: 0;
}

/* ── Panel ── */
.panel {
  display: flex;
  flex-direction: column;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--surface);
  min-height: 0;
}

/* Panel header – fixed height so both panels are identical */
.panel-header {
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 0.75rem;
  border-bottom: 1px solid var(--border);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  background: var(--bg);
  flex-shrink: 0;
}

/* ── Copy button ── */
#copy-btn {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  background: #238636;
  color: #fff;
  border: 1px solid #2ea043;
  border-radius: var(--radius);
  padding: 0.25rem 0.7rem;
  font-size: 0.75rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
  line-height: 1;
  white-space: nowrap;
}

#copy-btn svg {
  width: 13px;
  height: 13px;
  fill: currentColor;
  flex-shrink: 0;
}

#copy-btn:hover {
  background: #2ea043;
  border-color: #3fb950;
}

#copy-btn.copied {
  background: #1f6feb;
  border-color: #388bfd;
}

/* ── Overlay editor (left panel) ── */
.editor-wrap {
  position: relative;
  flex: 1;
  overflow: auto;
}

.editor-wrap pre {
  position: absolute;
  inset: 0;
  margin: 0;
  overflow: hidden;
  pointer-events: none;
}

.editor-wrap pre code {
  display: block;
  padding: var(--pad);
  font-family: var(--font-mono);
  font-size: var(--font-size);
  line-height: var(--line-height);
  background: transparent;
  white-space: pre;
  color: transparent;
}

textarea#input {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  background: transparent;
  color: transparent;
  caret-color: var(--text);
  border: none;
  outline: none;
  resize: none;
  padding: var(--pad);
  font-family: var(--font-mono);
  font-size: var(--font-size);
  line-height: var(--line-height);
  tab-size: 2;
  overflow: hidden;
  white-space: pre;
  word-wrap: normal;
}

textarea#input::placeholder {
  color: var(--text-muted);
}

/* ── Output panel (right) ── */
.panel > pre {
  flex: 1;
  overflow: auto;
  margin: 0;
}

.panel > pre code#output {
  display: block;
  padding: var(--pad);
  font-family: var(--font-mono);
  font-size: var(--font-size);
  line-height: var(--line-height);
  background: var(--surface);
  min-height: 100%;
  white-space: pre;
}

code#output.error {
  color: #e06c75;
}

/* ── Responsive ── */
@media (max-width: 768px) {
  body { overflow: auto; }
  main {
    grid-template-columns: 1fr;
    grid-template-rows: 50vh 50vh;
    height: auto;
  }
}