/* Reset, tokens e tema */
* { box-sizing: border-box; }
html, body { height: 100%; }
:root{
  --bg: #f6f8fb;
  --bg-accent: #eef2f7;
  --text: #0f172a;
  --muted: #475569;
  --surface: #ffffff;
  --border: rgba(15,23,42,.10);
  --shadow: 0 4px 16px rgba(15,23,42,.06);
  --shadow-lg: 0 10px 30px rgba(15,23,42,.14);
  --primary: #0ea5e9; /* sky-500 */
  --radius: 14px;
  --space: clamp(16px, 2vw, 24px);
}
.theme-dark:root,
body.theme-dark{
  --bg: #0b1220;
  --bg-accent: #0f172a;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --surface: #111827;
  --border: rgba(226,232,240,.12);
  --shadow: 0 4px 16px rgba(0,0,0,.35);
  --shadow-lg: 0 10px 30px rgba(0,0,0,.5);
  --primary: #38bdf8; /* sky-400 */
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  line-height: 1.5;
  color: var(--text);
  background: linear-gradient(180deg, var(--bg), var(--bg-accent));
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.container { width: min(1100px, 92%); margin: 0 auto; }

.site-header {
  position: sticky; top: 0; z-index: 10;
  background: linear-gradient(180deg, rgba(255,255,255,.65), rgba(255,255,255,.35));
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}
body.theme-dark .site-header{ background: linear-gradient(180deg, rgba(17,24,39,.7), rgba(17,24,39,.4)); }
.site-header .container{ display: flex; align-items: center; justify-content: space-between; padding: .9rem 0; }
.brand-title{ margin: 0; font-size: clamp(1.35rem, 2.5vw, 1.85rem); }
.subtitle{ margin: .15rem 0 0; color: var(--muted); font-size: .95rem; }
.site-nav{ display: flex; align-items: center; gap: .75rem; }
.nav-link{ text-decoration: none; color: var(--muted); padding: .5rem .75rem; border-radius: 10px; }
.nav-link:hover{ background: rgba(14,165,233,.08); color: var(--text); }
.theme-toggle{ border: 1px solid var(--border); background: var(--surface); color: var(--text); border-radius: 999px; padding: .45rem .6rem; cursor: pointer; box-shadow: var(--shadow); }
.theme-toggle:hover{ transform: translateY(-1px); box-shadow: var(--shadow-lg); }

/* Classe utilitária para leitores de tela */
.visually-hidden { position: absolute !important; height: 1px; width: 1px; overflow: hidden; clip: rect(1px, 1px, 1px, 1px); white-space: nowrap; }

/* Hero / Demonstração */
.hero-section{ padding: 1.25rem 0 0; }
.flex-container {
  display: flex;              /* Requisito: usar flexbox */
  justify-content: center;    /* Requisito: centraliza horizontalmente */
  align-items: center;        /* Requisito: centraliza verticalmente */
  min-height: 70vh;           /* Requisito: altura mínima visível */
  gap: 1.25rem;
  padding: 1.25rem;
  flex-wrap: wrap;            /* Responsivo em telas pequenas */
}

/* As três caixas */
.box {
  width: 160px;
  height: 160px;
  border-radius: var(--radius);
  display: flex; align-items: center; justify-content: center;
  font-weight: 700;
  color: var(--text);
  background: var(--surface);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  transition: transform 160ms ease, box-shadow 160ms ease;
}
.box:hover { transform: translateY(-4px); box-shadow: var(--shadow-lg); }
.box:focus-visible { outline: 3px solid var(--primary); outline-offset: 3px; }

/* Cores suaves por caixa */
.flex-container .box:nth-of-type(1) { background: linear-gradient(135deg, #e0f2fe, #f0f9ff); }
.flex-container .box:nth-of-type(2) { background: linear-gradient(135deg, #dcfce7, #f0fdf4); }
.flex-container .box:nth-of-type(3) { background: linear-gradient(135deg, #fee2e2, #fff7ed); }

/* Playground */
.playground{ padding: 2rem 0; }
.lead{ color: var(--muted); margin-top: .25rem; }
.controls{ margin-top: 1rem; display: grid; grid-template-columns: repeat(3, minmax(180px, 1fr)); gap: 1rem; align-items: end; }
.control-group{ display: grid; gap: .4rem; }
label{ color: var(--text); font-weight: 600; }
select, input[type="range"]{ width: 100%; padding: .6rem .7rem; border-radius: 10px; border: 1px solid var(--border); background: var(--surface); color: var(--text); }
.control-actions{ display: flex; gap: .6rem; align-items: center; }
.btn{ padding: .65rem .9rem; border-radius: 10px; border: 1px solid var(--border); background: var(--surface); color: var(--text); cursor: pointer; }
.btn.primary{ background: var(--primary); color: white; border-color: transparent; }
.btn:hover{ transform: translateY(-1px); box-shadow: var(--shadow); }
.help, .muted{ color: var(--muted); }

/* Código */
.code-section{ padding: 1rem 0 2rem; }
pre{ background: var(--surface); border: 1px solid var(--border); box-shadow: var(--shadow); padding: 1rem; border-radius: 12px; overflow: auto; }
code{ font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; font-size: .95rem; color: var(--text); }

.page-footer { text-align: center; padding: 1.25rem; color: var(--muted); }

@media (max-width: 900px){ .controls{ grid-template-columns: repeat(2, minmax(180px, 1fr)); } }
@media (max-width: 560px) {
  .flex-container { min-height: 60vh; gap: .75rem; }
  .box { width: 120px; height: 120px; font-size: .95rem; }
  .controls{ grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) { .box { transition: none; } .btn:hover, .theme-toggle:hover{ transform: none; } }