/* ===== VARIABLES ===== */
:root {
  --bg: #fff;
  --surface: #f5f5f7;
  --card: #fff;
  --border: #e0e0e6;
  --bh: #b0b0c8;
  --accent: #4f46e5;
  --accent2: #e8486a;
  --text: #111118;
  --muted: #6b6b85;
  --sh: 0 2px 12px rgba(0,0,0,0.07);
  --shh: 0 6px 24px rgba(79,70,229,0.13);
  --font: 'Aptos', 'Segoe UI', Arial, sans-serif;
  --mono: 'Courier New', monospace;
}

/* ===== RESET ===== */
* { margin: 0; padding: 0; box-sizing: border-box; }

/* ===== BODY - background image ===== */
body {
  background-color: var(--bg);
  background-image: url('BACK.jpg');
  background-size: cover;
  background-attachment: fixed;
  background-position: center;
  color: var(--text);
  font-family: var(--font);
  min-height: 100vh;
  overflow-x: hidden;
}

/* ===== NAV ===== */
nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  padding: 0 2rem;
  height: 58px;
  box-shadow: 0 1px 8px rgba(0,0,0,0.06);
}

.nav-logo {
  font-size: 1.15rem;
  font-weight: 800;
  letter-spacing: -.03em;
  margin-right: auto;
  display: flex;
  align-items: center;
  gap: .6rem;
}
.nav-logo span { color: var(--accent); }

.nav-img {
  height: 34px;
  width: 34px;
  object-fit: cover;
  border-radius: 8px;
  border: 1px solid var(--border);
}

.nav-btn {
  background: none;
  border: none;
  color: var(--muted);
  font-family: var(--font);
  font-size: .85rem;
  font-weight: 600;
  letter-spacing: .04em;
  text-transform: uppercase;
  padding: 0 1.2rem;
  height: 58px;
  cursor: pointer;
  transition: color .2s;
  border-bottom: 2px solid transparent;
}
.nav-btn.active { color: var(--accent); border-bottom-color: var(--accent); }
.nav-btn:hover { color: var(--text); }

/* ===== PAGE SYSTEM ===== */
.page { display: none; }
.page.active { display: block; }

/* ===== HERO ===== */
.hero {
  padding: 4rem 2rem 2.5rem;
  text-align: center;
  background: linear-gradient(180deg, rgba(240,239,255,0.95), rgba(255,255,255,0.95));
  border-bottom: 1px solid var(--border);
}
.hero-label {
  display: inline-block;
  font-size: .72rem;
  font-weight: 600;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--accent);
  background: rgba(79,70,229,.08);
  border: 1px solid rgba(79,70,229,.2);
  padding: .35rem 1rem;
  border-radius: 100px;
  margin-bottom: 1.4rem;
}
.hero h1 {
  font-size: clamp(2.2rem, 5.5vw, 4.2rem);
  font-weight: 800;
  letter-spacing: -.04em;
  line-height: 1.08;
  margin-bottom: 1rem;
}
.hero h1 em { color: var(--accent); font-style: normal; }
.hero p { color: var(--muted); font-size: 1rem; max-width: 480px; margin: 0 auto; line-height: 1.7; }

/* ===== LAYOUT ===== */
.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2.5rem 2rem 5rem;
  background: rgba(255,255,255,0.88);
  backdrop-filter: blur(8px);
}

.sec {
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 1.25rem;
  padding-bottom: .7rem;
  border-bottom: 1.5px solid var(--border);
}
.sec span { color: var(--accent); }

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(310px, 1fr));
  gap: 1.25rem;
  margin-bottom: 2.5rem;
}

/* ===== CARDS ===== */
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.6rem;
  transition: border-color .25s, box-shadow .25s, transform .25s;
  box-shadow: var(--sh);
}
.card:hover { border-color: var(--bh); box-shadow: var(--shh); transform: translateY(-2px); }
.card.wide { grid-column: 1 / -1; }

.card-tag {
  font-size: .62rem;
  font-weight: 700;
  letter-spacing: .16em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: .6rem;
}
.card h3 { font-size: 1.05rem; font-weight: 700; margin-bottom: .45rem; }
.card p { color: var(--muted); font-size: .84rem; line-height: 1.6; margin-bottom: 1.1rem; }

/* ===== FORMULA BOX ===== */
.fbox {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: .85rem 1.1rem;
  font-family: var(--mono);
  font-size: .88rem;
  color: var(--accent);
  margin-bottom: 1.1rem;
}

/* ===== INPUTS ===== */
.row { display: flex; gap: .5rem; flex-wrap: wrap; margin-bottom: .7rem; }

input[type=text], input[type=number], select {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 7px;
  color: var(--text);
  font-family: var(--font);
  font-size: .85rem;
  padding: .5rem .85rem;
  flex: 1;
  min-width: 75px;
  outline: none;
  transition: border-color .2s, box-shadow .2s;
}
input:focus, select:focus { border-color: var(--accent); box-shadow: 0 0 0 3px rgba(79,70,229,.1); }
input::placeholder { color: #b0b0c0; }

label.lbl { font-size: .7rem; font-weight: 600; color: var(--muted); display: block; margin-bottom: .25rem; }
.ig { flex: 1; min-width: 75px; }

/* ===== BUTTONS ===== */
.btn {
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 7px;
  padding: .55rem 1.1rem;
  font-family: var(--font);
  font-size: .82rem;
  font-weight: 700;
  cursor: pointer;
  transition: opacity .18s, transform .15s;
  box-shadow: 0 2px 8px rgba(79,70,229,.18);
}
.btn:hover { opacity: .88; transform: translateY(-1px); }
.btn.sec { background: var(--surface); border: 1px solid var(--border); color: var(--text); box-shadow: none; }

/* ===== RESULT BOXES ===== */
.res {
  margin-top: .7rem;
  padding: .7rem .95rem;
  border-radius: 7px;
  font-family: var(--mono);
  font-size: .82rem;
  background: rgba(79,70,229,.06);
  border: 1px solid rgba(79,70,229,.18);
  color: #3730a3;
  white-space: pre-line;
  display: none;
  animation: fi .25s ease;
}
.res.show { display: block; }
.res.err { background: rgba(232,72,106,.07); border-color: rgba(232,72,106,.25); color: #b91c44; }
.res.ok  { background: rgba(14,168,122,.07); border-color: rgba(14,168,122,.25); color: #065f46; }

@keyframes fi {
  from { opacity: 0; transform: translateY(3px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ===== SOLVER ===== */
.solver {
  background: linear-gradient(135deg, #f0efff, #fff 60%);
  border: 1px solid rgba(79,70,229,.2);
  border-radius: 14px;
  padding: 1.8rem;
  margin-bottom: 2.5rem;
  box-shadow: var(--sh);
}
.solver h2 { font-size: 1.3rem; font-weight: 800; margin-bottom: .35rem; }
.solver p  { color: var(--muted); font-size: .85rem; margin-bottom: 1.4rem; }

.srow { display: flex; gap: .7rem; align-items: center; }
.srow input { font-size: .95rem; padding: .7rem 1rem; flex: 1; }

.chips { display: flex; flex-wrap: wrap; gap: .45rem; margin-top: .7rem; }
.chip {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 100px;
  padding: .28rem .75rem;
  font-family: var(--mono);
  font-size: .7rem;
  color: var(--muted);
  cursor: pointer;
  transition: border-color .18s, color .18s;
}
.chip:hover { border-color: var(--accent); color: var(--accent); }

/* ===== DIVIDER ===== */
.div { height: 1px; background: linear-gradient(90deg, transparent, var(--border), transparent); margin: 2rem 0; }

/* ===== EXERCICES PAGE ===== */
.ex-hero {
  padding: 3.5rem 2rem 2rem;
  text-align: center;
  background: linear-gradient(180deg, rgba(255,240,243,0.95), rgba(255,255,255,0.95));
  border-bottom: 1px solid var(--border);
}
.ex-hero h1 { font-size: clamp(1.8rem, 4.5vw, 3rem); font-weight: 800; letter-spacing: -.03em; }
.ex-hero h1 em { color: var(--accent2); font-style: normal; }
.ex-hero p { color: var(--muted); margin-top: .6rem; font-size: .88rem; }

.ex-grid {
  display: grid;
  gap: 1.5rem;
  max-width: 780px;
  margin: 0 auto;
  padding: 2rem 2rem 5rem;
}

.ex-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.8rem;
  box-shadow: var(--sh);
}

.ex-num {
  font-size: .62rem;
  font-weight: 700;
  letter-spacing: .18em;
  color: var(--accent2);
  text-transform: uppercase;
  margin-bottom: .45rem;
}
.ex-card h3 { font-size: 1.05rem; font-weight: 700; margin-bottom: .65rem; }
.ex-card p.desc { color: var(--muted); font-size: .84rem; margin-bottom: 1.1rem; line-height: 1.6; }

/* ===== GAME ===== */
.gdisp {
  font-family: var(--mono);
  font-size: 2.2rem;
  font-weight: 700;
  color: var(--accent);
  text-align: center;
  padding: 1.3rem;
  background: var(--surface);
  border-radius: 10px;
  margin-bottom: 1rem;
  border: 1px solid var(--border);
}
.gbtns { display: flex; gap: .7rem; justify-content: center; margin-bottom: 1rem; }
.ghist, .gatt { font-family: var(--mono); font-size: .73rem; color: var(--muted); text-align: center; margin-top: .4rem; }

/* ===== QCM ===== */
.qq { margin-bottom: 1.4rem; }
.qq h4 { font-size: .92rem; font-weight: 600; margin-bottom: .65rem; line-height: 1.5; }
.tf { display: flex; gap: .7rem; }

.qres {
  padding: 1rem 1.1rem;
  border-radius: 9px;
  background: rgba(79,70,229,.06);
  border: 1px solid rgba(79,70,229,.2);
  font-size: .88rem;
  display: none;
  margin-top: 1rem;
  line-height: 1.7;
}
.qres.show { display: block; animation: fi .25s; }

/* ===== RESPONSIVE ===== */
@media (max-width: 600px) {
  .srow { flex-direction: column; }
  .grid { grid-template-columns: 1fr; }
  .gbtns { flex-direction: column; }
}