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

:root {
  --bg:          #0d0f14;
  --bg2:         #13161e;
  --bg3:         #1a1d27;
  --border:      rgba(255,255,255,0.07);
  --border-md:   rgba(255,255,255,0.13);
  --accent:      #7c6af7;
  --accent2:     #a78bfa;
  --accent-glow: rgba(124,106,247,0.16);
  --green:       #34d399;
  --green-glow:  rgba(52,211,153,0.12);
  --text:        #e8e6f0;
  --text2:       #9896a8;
  --text3:       #5f5d70;
  --mono:        'DM Mono', monospace;
  --serif:       'DM Serif Display', serif;
  --sans:        'Figtree', sans-serif;
  --radius:      12px;
  --radius-sm:   8px;
}

html { scroll-behavior: smooth; }
body { font-family: var(--sans); background: var(--bg); color: var(--text); min-height: 100vh; line-height: 1.6; }

/* ── FONDO ── */
.bg-grid {
  position: fixed; inset: 0; pointer-events: none; z-index: 0;
  background-image: linear-gradient(rgba(124,106,247,0.025) 1px, transparent 1px), linear-gradient(90deg, rgba(124,106,247,0.025) 1px, transparent 1px);
  background-size: 40px 40px;
}
.bg-glow {
  position: fixed; top: -220px; left: 50%; transform: translateX(-50%);
  width: 900px; height: 600px; pointer-events: none; z-index: 0;
  background: radial-gradient(ellipse, rgba(124,106,247,0.09) 0%, transparent 68%);
}

/* ── HEADER ── */
.header {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; justify-content: space-between;
  padding: 1.2rem 2rem;
  border-bottom: 1px solid var(--border);
  background: rgba(13,15,20,0.85);
  backdrop-filter: blur(14px);
}
.logo { display: flex; align-items: center; gap: 10px; text-decoration: none; }
.logo-symbol { font-family: var(--serif); font-size: 28px; color: var(--accent2); line-height: 1; }
.logo-text   { font-family: var(--serif); font-size: 20px; color: var(--text); letter-spacing: -0.02em; }
.header-tagline { font-size: 12px; color: var(--text3); letter-spacing: 0.04em; }
.header nav { display: flex; gap: 4px; }
.header nav a {
  font-size: 13px; color: var(--text3); text-decoration: none;
  padding: 6px 12px; border-radius: var(--radius-sm);
  transition: color 0.18s, background 0.18s;
}
.header nav a:hover { color: var(--text2); background: var(--bg3); }

/* ── HERO ── */
.hero {
  position: relative; z-index: 10;
  text-align: center; padding: 72px 24px 60px;
}
.hero-tag {
  display: inline-block; font-size: 11px; font-weight: 600;
  letter-spacing: 0.09em; text-transform: uppercase;
  color: var(--accent2); background: var(--accent-glow);
  border: 1px solid rgba(124,106,247,0.28);
  padding: 4px 14px; border-radius: 999px; margin-bottom: 20px;
}
.hero h1 {
  font-family: var(--serif); font-size: 48px; line-height: 1.2;
  color: var(--text); margin-bottom: 16px; font-style: italic;
}
.hero p { font-size: 16px; color: var(--text2); max-width: 480px; margin: 0 auto 32px; }
.hero-btn {
  display: inline-block; background: var(--accent); color: white;
  padding: 13px 32px; border-radius: var(--radius-sm); font-weight: 600;
  font-size: 15px; text-decoration: none;
  box-shadow: 0 0 28px rgba(124,106,247,0.28);
  transition: opacity 0.18s;
}
.hero-btn:hover { opacity: 0.88; }

/* ── MAIN (index) ── */
.main {
  position: relative; z-index: 10;
  max-width: 900px; margin: 0 auto;
  padding: 2.5rem 1.5rem 5rem;
  display: flex; flex-direction: column; gap: 2.5rem;
}

/* ── SECCIÓN ── */
.section-label {
  font-size: 10.5px; font-weight: 600; color: var(--text3);
  letter-spacing: 0.09em; text-transform: uppercase;
  display: flex; align-items: center; gap: 10px; margin-bottom: 14px;
}
.section-label::after { content: ''; flex: 1; height: 1px; background: var(--border); }

/* ── GRID DE TARJETAS ── */
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 10px; }
.card {
  background: var(--bg2); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 18px 16px;
  text-decoration: none; color: var(--text);
  transition: border-color 0.18s, transform 0.18s, background 0.18s;
  display: block;
}
.card:hover { border-color: var(--accent); background: rgba(124,106,247,0.05); transform: translateY(-2px); }
.card-icon { font-family: var(--mono); font-size: 13px; color: var(--accent); margin-bottom: 10px; }
.card h3 { font-size: 14px; font-weight: 600; margin-bottom: 6px; color: var(--text); }
.card p  { font-size: 12px; color: var(--text3); line-height: 1.55; }

/* ── GENERADOR (MathGen standalone) ── */
.config-panel {
  background: var(--bg2); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1.5rem;
  display: flex; flex-direction: column; gap: 1.4rem;
}
.config-title {
  font-size: 10.5px; font-weight: 600; color: var(--text3);
  letter-spacing: 0.09em; text-transform: uppercase; margin-bottom: 9px;
}
.config-row { display: grid; grid-template-columns: 1fr 1fr; gap: 1.4rem; }

.topics-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); gap: 6px; }
.topic-btn {
  background: var(--bg3); border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 9px 12px; font-family: var(--sans); font-size: 13px; color: var(--text2);
  cursor: pointer; text-align: left; transition: all 0.18s;
  display: flex; align-items: center; gap: 8px;
}
.topic-btn:hover { border-color: var(--border-md); color: var(--text); background: rgba(124,106,247,0.05); }
.topic-btn.active { border-color: var(--accent); background: var(--accent-glow); color: var(--accent2); font-weight: 500; }
.topic-icon { font-family: var(--mono); font-size: 11px; color: var(--accent); min-width: 24px; text-align: center; }

.diff-group { display: flex; gap: 6px; flex-wrap: wrap; }
.diff-btn {
  background: var(--bg3); border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 7px 16px; font-family: var(--sans); font-size: 13px; color: var(--text2); cursor: pointer; transition: all 0.18s;
}
.diff-btn:hover { border-color: var(--border-md); color: var(--text); }
.diff-btn.active { border-color: var(--accent); background: var(--accent-glow); color: var(--accent2); font-weight: 500; }

.gen-btn {
  background: var(--accent); border: none; border-radius: var(--radius-sm);
  padding: 12px 28px; font-family: var(--sans); font-size: 15px; font-weight: 600;
  color: white; cursor: pointer; display: flex; align-items: center; gap: 8px;
  transition: opacity 0.18s, transform 0.1s;
  box-shadow: 0 0 28px rgba(124,106,247,0.28);
}
.gen-btn:hover { opacity: 0.88; }
.gen-btn:active { transform: scale(0.98); }

.exercise-section {
  background: var(--bg2); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 2rem; min-height: 200px;
}
.empty-state { display: flex; flex-direction: column; align-items: center; justify-content: center; gap: 12px; min-height: 160px; color: var(--text3); }
.empty-icon { font-family: var(--serif); font-size: 60px; color: var(--border-md); line-height: 1; }
.empty-state p { font-size: 14px; }

/* ── EJERCICIO ── */
.ex-header { display: flex; align-items: flex-start; justify-content: space-between; gap: 12px; margin-bottom: 1.25rem; }
.ex-meta { display: flex; gap: 6px; flex-wrap: wrap; }
.badge { font-size: 11px; font-weight: 600; letter-spacing: 0.05em; padding: 4px 10px; border-radius: 999px; text-transform: uppercase; }
.badge-topic { background: var(--accent-glow); color: var(--accent2); border: 1px solid rgba(124,106,247,0.28); }
.badge-diff  { background: var(--bg3); color: var(--text2); border: 1px solid var(--border); }
.badge.basico     { background: rgba(52,211,153,0.12); color: #34d399; border: 1px solid rgba(52,211,153,0.2); }
.badge.intermedio { background: rgba(251,191,36,0.1);  color: #fbbf24; border: 1px solid rgba(251,191,36,0.2); }
.badge.avanzado   { background: rgba(248,113,113,0.1); color: #f87171; border: 1px solid rgba(248,113,113,0.2); }

.new-btn { background: transparent; border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 6px 14px; font-size: 12px; color: var(--text3); cursor: pointer; transition: all 0.18s; white-space: nowrap; }
.new-btn:hover { border-color: var(--border-md); color: var(--text2); }

.ex-question { font-family: var(--serif); font-size: 21px; line-height: 1.55; color: var(--text); margin-bottom: 1.4rem; font-style: italic; }
.divider { height: 1px; background: var(--border); margin: 1.25rem 0; }

/* ── SOLUCIÓN ── */
.sol-toggle {
  display: flex; align-items: center; gap: 8px; background: transparent;
  border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 10px 18px; font-family: var(--sans); font-size: 13px; color: var(--text2); cursor: pointer; transition: all 0.18s;
}
.sol-toggle:hover { border-color: var(--accent); color: var(--accent2); }
.sol-toggle.open { border-color: var(--accent); color: var(--accent2); background: var(--accent-glow); }
.sol-arrow { transition: transform 0.2s; }
.sol-toggle.open .sol-arrow { transform: rotate(180deg); }

.solution-box { margin-top: 1.25rem; display: none; flex-direction: column; animation: fadeIn 0.25s ease; }
.solution-box.open { display: flex; }
@keyframes fadeIn { from { opacity:0; transform:translateY(-6px); } to { opacity:1; transform:translateY(0); } }

.step { display: flex; gap: 14px; padding: 14px 0; border-bottom: 1px solid var(--border); }
.step:last-child { border-bottom: none; }
.step-num {
  width: 26px; height: 26px; min-width: 26px; background: var(--accent); color: white;
  border-radius: 50%; display: flex; align-items: center; justify-content: center;
  font-family: var(--mono); font-size: 11px; font-weight: 500; margin-top: 2px;
}
.step-body { flex: 1; }
.step-title { font-size: 13px; font-weight: 600; color: var(--text); margin-bottom: 4px; }
.step-text  { font-size: 13px; color: var(--text2); line-height: 1.65; }
.step-formula {
  display: block; margin-top: 8px; font-family: var(--mono); font-size: 13px; color: var(--accent2);
  background: var(--bg3); border: 1px solid var(--border); border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 8px 14px; white-space: pre-wrap; word-break: break-word;
}
.answer-box {
  margin-top: 1.25rem; background: var(--accent-glow);
  border: 1px solid rgba(124,106,247,0.28); border-radius: var(--radius-sm);
  padding: 12px 18px; display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
}
.answer-label { font-size: 10.5px; font-weight: 600; letter-spacing: 0.07em; color: var(--accent); text-transform: uppercase; white-space: nowrap; }
.answer-value { font-family: var(--mono); font-size: 15px; color: var(--accent2); font-weight: 500; }

/* ── ACERCA ── */
.about-box {
  background: var(--bg2); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 2rem;
}
.about-box h2 { font-family: var(--serif); font-size: 22px; color: var(--text); margin-bottom: 12px; font-style: italic; }
.about-box p  { font-size: 14px; color: var(--text2); line-height: 1.8; max-width: 580px; }

/* ── FOOTER ── */
.footer { position: relative; z-index: 10; text-align: center; padding: 1.5rem; font-size: 11px; color: var(--text3); border-top: 1px solid var(--border); letter-spacing: 0.05em; }

/* ── SCROLLBAR ── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--bg3); border-radius: 3px; }

/* ── RESPONSIVE ── */
@media (max-width: 600px) {
  .hero h1 { font-size: 32px; }
  .grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 580px) {
  .config-row { grid-template-columns: 1fr; }
}
@media (max-width: 400px) {
  .grid { grid-template-columns: 1fr; }
}

/* ── MODO CLARO ── */
body.light-mode {
  --bg:          #ffffff;
  --bg2:         #f4f4f8;
  --bg3:         #eaeaf0;
  --border:      rgba(0,0,0,0.08);
  --border-md:   rgba(0,0,0,0.15);
  --text:        #1a1a2e;
  --text2:       #4a4a6a;
  --text3:       #8888aa;
  --accent-glow: rgba(124,106,247,0.08);
}
body.light-mode .bg-grid {
  background-image:
    linear-gradient(rgba(124,106,247,0.05) 1px, transparent 1px),
    linear-gradient(90deg, rgba(124,106,247,0.05) 1px, transparent 1px);
}
body.light-mode header {
  background: rgba(255,255,255,0.9);
}
body.light-mode .bg-glow { opacity: 0.4; }

#theme-btn {
  background: transparent;
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-radius: 8px;
  padding: 3px 5px;
  cursor: pointer;
  color: #ffffff;
  display: flex;
  align-items: center;
  transition: background 0.2s, border-color 0.2s;
}

#theme-btn .material-symbols-rounded {
  font-size: 18px;
}

#theme-btn:hover {
  background: rgba(255, 255, 255, 0.1);
  border-color: rgba(255, 255, 255, 0.6);
}

body.light-mode #theme-btn {
  color: #111111;
  border-color: rgba(0, 0, 0, 0.3);
}

body.light-mode #theme-btn:hover {
  background: rgba(0, 0, 0, 0.08);
  border-color: rgba(0, 0, 0, 0.6);
}