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

:root {
  --bg: #fff;
  --bg-2: #f8f8f8;
  --text: #111;
  --text-2: #444;
  --text-3: #888;
  --border: #e5e5e5;
  --font: system-ui, -apple-system, sans-serif;
  --mono: 'Menlo', 'Monaco', monospace;
}

body { font-family: var(--font); background: var(--bg); color: var(--text); }

nav { padding: 20px 40px; border-bottom: 1px solid var(--border); }
nav a { font-size: 0.8125rem; color: var(--text-3); text-decoration: none; }
nav a:hover { color: var(--text); }

main { max-width: 800px; margin: 0 auto; padding: 0 40px 80px; }

.page-header { padding: 60px 0 48px; border-bottom: 1px solid var(--border); margin-bottom: 40px; }
.label { font-size: 0.72rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--text-3); margin-bottom: 16px; }
h1 { font-size: 2rem; letter-spacing: -0.03em; margin-bottom: 12px; }
.sub { font-size: 0.9375rem; color: var(--text-2); }

/* Variants */
.variants { display: flex; flex-direction: column; gap: 0; }
.variant { padding: 28px 0; border-bottom: 1px solid var(--border); }

.variant-meta { display: flex; align-items: center; gap: 10px; margin-bottom: 16px; }
.variant-num { font-family: var(--mono); font-size: 0.75rem; color: var(--text-3); }
.variant-quality { font-size: 0.7rem; font-weight: 600; letter-spacing: 0.06em; text-transform: uppercase; padding: 2px 8px; border-radius: 3px; }
.variant-quality.bad { background: #fef2f2; color: #dc2626; }
.variant-quality.ok { background: #fff7ed; color: #c2410c; }
.variant-quality.good { background: #f0fdf4; color: #16a34a; }
.variant-quality.great { background: #eff6ff; color: #2563eb; }

.prompt-box { background: var(--bg-2); border: 1px solid var(--border); border-radius: 6px; padding: 14px 16px; margin-bottom: 14px; }
.prompt-label { font-size: 0.65rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; color: var(--text-3); margin-bottom: 8px; }
.prompt-text { font-family: var(--mono); font-size: 0.8rem; color: var(--text); line-height: 1.6; display: block; white-space: pre-wrap; word-break: break-word; }

.result-box { margin-bottom: 12px; }
.result-label { font-size: 0.65rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; color: var(--text-3); margin-bottom: 12px; }
.result-demo { display: flex; align-items: center; min-height: 48px; }
.result-demo.row { gap: 12px; flex-wrap: wrap; }

.problem { font-size: 0.8125rem; color: var(--text-3); font-style: italic; }

/* Button variants */
.v1-btn { /* browser default — intentionally unstyled */ cursor: pointer; }

.v2-btn {
  background: #2563eb;
  color: #fff;
  border: none;
  padding: 12px 24px;
  cursor: pointer;
  font-size: 1rem;
}

.v3-btn {
  background: #2563eb;
  color: #fff;
  border: none;
  padding: 12px 24px;
  border-radius: 6px;
  font-size: 0.9375rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s ease;
  font-family: inherit;
}
.v3-btn:hover { background: #1d4ed8; }

.v4-btn {
  background: #2563eb;
  color: #fff;
  border: none;
  padding: 12px 24px;
  border-radius: 6px;
  font-size: 0.9375rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s ease;
  font-family: inherit;
  outline: none;
}
.v4-btn:hover { background: #1d4ed8; }
.v4-btn:active { background: #1e40af; }
.v4-btn:focus-visible { outline: 2px solid #2563eb; outline-offset: 2px; }

.v5-btn {
  background: #dc2626;
  color: #fff;
  border: none;
  padding: 10px 20px;
  border-radius: 6px;
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s ease;
  font-family: inherit;
  outline: none;
}
.v5-btn:hover:not(:disabled) { background: #b91c1c; }
.v5-btn:active:not(:disabled) { background: #991b1b; }
.v5-btn:focus-visible { outline: 2px solid #dc2626; outline-offset: 2px; }
.v5-btn:disabled { opacity: 0.4; cursor: not-allowed; }

/* Formula */
.formula { padding: 48px 0 0; }
h2 { font-size: 1.1rem; margin-bottom: 24px; }
.formula-parts {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr auto 1fr;
  gap: 0;
  align-items: center;
}
.formula-part {
  padding: 20px;
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  text-align: center;
}
.formula-label { font-size: 0.8125rem; font-weight: 600; margin-bottom: 6px; }
.formula-desc { font-size: 0.75rem; color: var(--text-3); line-height: 1.5; }
.plus { font-size: 1.25rem; color: var(--text-3); padding: 0 12px; }

@media (max-width: 640px) {
  nav { padding: 16px 20px; }
  main { padding: 0 20px 60px; }
  .formula-parts { grid-template-columns: 1fr; }
  .plus { display: none; }
  .formula-part { margin-bottom: 8px; }
}