:root {
  --bg: #f4f4f2;
  --fg: #16161a;
  --muted: #6b6b70;
  --line: rgba(0,0,0,0.1);
  --accent: #16161a;
}
* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; height: 100%; }
body {
  background: var(--bg);
  color: var(--fg);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  display: flex;
  flex-direction: column;
}
header {
  padding: 14px 20px 10px;
  border-bottom: 1px solid var(--line);
  background: var(--bg);
  flex: none;
}
header h1 {
  margin: 0 0 2px;
  font-size: 15px;
  font-weight: 600;
  letter-spacing: -0.01em;
}
header p {
  margin: 0;
  font-size: 12px;
  color: var(--muted);
}
nav.tabs {
  display: flex;
  gap: 4px;
  padding: 0 20px;
  border-bottom: 1px solid var(--line);
  background: var(--bg);
  flex: none;
  overflow-x: auto;
}
nav.tabs button {
  appearance: none;
  border: none;
  background: transparent;
  font: inherit;
  font-size: 13px;
  font-weight: 500;
  color: var(--muted);
  padding: 10px 16px;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  white-space: nowrap;
  transition: color 0.15s ease, border-color 0.15s ease;
}
nav.tabs button .tone {
  display: inline-block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  margin-right: 7px;
  vertical-align: middle;
}
nav.tabs button .sub {
  opacity: .55;
  font-weight: 400;
  margin-left: 6px;
  font-size: 11px;
}
nav.tabs button:hover { color: var(--fg); }
nav.tabs button.active {
  color: var(--fg);
  border-bottom-color: var(--accent);
}
main {
  flex: 1;
  position: relative;
  min-height: 0;
}
.pane {
  position: absolute;
  inset: 0;
  display: none;
}
.pane.active { display: block; }
.pane iframe {
  width: 100%;
  height: 100%;
  border: none;
  display: block;
  background: #fff;
}
.pane .placeholder {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
  color: var(--muted);
  font-size: 13px;
}