:root{--blue:#1e3a8a;--blue-light:#3b82f6;--blue-bg:#eff6ff;--blue-dark:#1e40af;--green:#10b981;--green-dark:#047857;--green-bg:#ecfdf5;--red:#ef4444;--red-bg:#fef2f2;--slate:#1e293b;--slate-light:#475569;--slate-lighter:#64748b;--bg:#f8fafc;--card:#ffffff;--border:#e2e8f0;--shadow:0 1px 3px rgba(0,0,0,0.06);--radius:12px}
*{box-sizing:border-box;margin:0;padding:0}
html,body{background:var(--bg);color:var(--slate);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,'Helvetica Neue',Arial,sans-serif;line-height:1.6;-webkit-font-smoothing:antialiased}
.wrap{max-width:920px;margin:0 auto;padding:0 16px}
.topbar{display:flex;justify-content:space-between;align-items:center;background:#fff;margin:0 0 24px;padding:14px 16px;border-radius:0 0 var(--radius) var(--radius);border-bottom:1px solid var(--border);gap:12px;flex-wrap:wrap}
.brand{display:flex;gap:12px;align-items:center;text-decoration:none;color:var(--blue)}
.brand-flag{font-size:28px}
.brand-text strong{display:block;color:var(--blue);font-size:15px}
.brand-text small{color:var(--slate-lighter);font-size:11px}
.topnav{display:flex;gap:14px;align-items:center;flex-wrap:wrap}
.topnav a{color:var(--slate-light);text-decoration:none;font-size:14px;font-weight:500}
.topnav a:hover{color:var(--blue)}
.topnav a.cta{background:var(--blue);color:#fff;padding:8px 14px;border-radius:8px;font-weight:600;font-size:14px}
.content{padding:0 0 40px}
.badge{display:inline-block;background:var(--blue-bg);color:var(--blue);padding:4px 10px;border-radius:6px;font-size:12px;font-weight:600;margin-right:6px;margin-bottom:8px}
h1{font-size:30px;line-height:1.2;color:var(--blue);margin:14px 0 10px;font-weight:800}
h2{font-size:22px;color:var(--blue);margin:28px 0 12px;font-weight:700}
h3{font-size:17px;color:var(--slate);margin:18px 0 8px;font-weight:600}
.en-line{color:var(--slate-lighter);font-size:14px;margin-bottom:18px;font-style:italic}
.lead{font-size:17px;color:var(--slate-light);margin-bottom:24px;line-height:1.7}
.crumbs{font-size:13px;color:var(--slate-lighter);margin-bottom:10px}
.crumbs a{color:var(--blue);text-decoration:none}
.crumbs a:hover{text-decoration:underline}

/* Buttons */
.btn{display:inline-flex;align-items:center;gap:6px;background:var(--card);color:var(--blue);border:1px solid var(--border);padding:10px 16px;border-radius:8px;font-size:14px;font-weight:600;cursor:pointer;font-family:inherit;text-decoration:none;transition:all 0.15s}
.btn:hover{background:var(--blue-bg);border-color:var(--blue)}
.btn-primary{background:var(--blue);color:#fff;border-color:var(--blue)}
.btn-primary:hover{background:var(--blue-dark);border-color:var(--blue-dark);color:#fff}
.btn-row{display:flex;gap:10px;flex-wrap:wrap;margin:16px 0}

/* Question page */
.qhead{display:flex;gap:6px;flex-wrap:wrap;margin-bottom:6px}
.flipcard{perspective:1000px;background:transparent;height:auto;min-height:200px;margin:18px 0;cursor:pointer}
.flipcard-inner{position:relative;width:100%;min-height:200px;text-align:center;transition:transform 0.6s;transform-style:preserve-3d}
.flipcard.flipped .flipcard-inner{transform:rotateY(180deg)}
.flipcard-front,.flipcard-back{position:absolute;top:0;left:0;width:100%;min-height:200px;backface-visibility:hidden;display:flex;flex-direction:column;justify-content:center;align-items:center;padding:28px 22px;border-radius:var(--radius);box-shadow:var(--shadow);border:2px solid var(--border)}
.flipcard-front{background:linear-gradient(135deg,#fff,#eff6ff);border-color:var(--blue)}
.flipcard-front h2{font-size:24px;color:var(--blue);margin:0 0 8px;line-height:1.3}
.flipcard-front .en{display:block;font-size:15px;color:var(--slate-lighter);font-style:italic;margin-top:10px}
.flipcard-back{background:linear-gradient(135deg,#ecfdf5,#d1fae5);border-color:var(--green);transform:rotateY(180deg)}
.flipcard-back .label{font-size:12px;font-weight:700;color:var(--green-dark);text-transform:uppercase;letter-spacing:1px;margin-bottom:12px}
.flipcard-back .answer{font-size:22px;font-weight:700;color:var(--slate);line-height:1.4;margin-bottom:14px}
.flipcard-back .en-answer{font-size:15px;color:var(--slate-lighter);font-style:italic}
.flipcard-hint{text-align:center;font-size:13px;color:var(--slate-lighter);margin-top:8px}

/* Sections */
.section{background:var(--card);padding:24px;border-radius:var(--radius);border:1px solid var(--border);margin:20px 0}
.section.tinted{background:var(--blue-bg);border-color:#bfdbfe}

/* Inline quiz */
.quiz{background:var(--card);padding:22px;border-radius:var(--radius);border:2px solid var(--border);margin:20px 0}
.quiz h3{color:var(--blue);margin-bottom:12px}
.quiz-question{font-size:17px;font-weight:600;color:var(--slate);margin-bottom:14px}
.quiz-choices{display:flex;flex-direction:column;gap:8px}
.quiz-choices button{background:var(--bg);border:2px solid var(--border);padding:12px 16px;border-radius:8px;text-align:left;cursor:pointer;font-size:15px;font-family:inherit;color:var(--slate);transition:all 0.15s}
.quiz-choices button:hover{border-color:var(--blue);background:var(--blue-bg)}
.quiz-choices button.correct{background:var(--green-bg);border-color:var(--green);color:var(--green-dark);font-weight:600}
.quiz-choices button.wrong{background:var(--red-bg);border-color:var(--red);color:#991b1b;text-decoration:line-through}
.quiz-feedback{margin-top:14px;padding:12px;border-radius:8px;font-size:14px;font-weight:500;display:none}
.quiz-feedback.ok{background:var(--green-bg);color:var(--green-dark);display:block}
.quiz-feedback.bad{background:var(--red-bg);color:#991b1b;display:block}

/* Progress bar */
.progress-card{background:linear-gradient(135deg,var(--blue),var(--blue-dark));color:#fff;padding:20px;border-radius:var(--radius);margin:20px 0}
.progress-card h3{color:#fff;font-size:15px;margin:0 0 10px}
.progress-bar-wrap{background:rgba(255,255,255,0.2);border-radius:99px;height:10px;overflow:hidden}
.progress-bar{background:#fff;height:100%;width:0;transition:width 0.3s}
.progress-stat{font-size:13px;color:#dbeafe;margin-top:8px}
.progress-stat strong{color:#fff;font-size:16px}

/* Q-list / nav */
.qlist,.qlist-compact{margin-left:24px;color:var(--slate-light)}
.qlist li,.qlist-compact li{margin:8px 0}
.qlist a,.qlist-compact a{color:var(--blue);text-decoration:none}
.qlist a:hover,.qlist-compact a:hover{text-decoration:underline}
.qlist a.studied::before{content:"✅ ";color:var(--green)}

.qnav{display:flex;justify-content:space-between;gap:16px;margin:32px 0;padding:18px 0;border-top:1px solid var(--border);border-bottom:1px solid var(--border)}
.qnav a{flex:1;color:var(--blue);text-decoration:none;padding:14px;background:var(--card);border-radius:8px;border:1px solid var(--border);font-size:14px;font-weight:500}
.qnav a:hover{background:var(--blue-bg)}
.qnav span{flex:1}

.hub-section{margin:28px 0;padding:22px;background:var(--card);border-radius:var(--radius);border:1px solid var(--border)}
.hub-section h2{margin-top:0;font-size:20px}
.hub-section h2 a{color:var(--blue);text-decoration:none}
.hub-section h2 small{color:var(--slate-lighter);font-weight:500;font-size:13px}
.hub-section h2 a.studied-count{color:var(--green-dark);font-weight:600}

.app-cta{background:linear-gradient(135deg,var(--blue),var(--blue-dark));color:#fff;padding:28px;border-radius:var(--radius);margin:32px 0;text-align:center}
.app-cta h3{color:#fff;margin:0 0 8px;font-size:22px}
.app-cta p{color:#dbeafe;margin-bottom:16px}
.app-cta .btn-primary{background:#fff;color:var(--blue);font-size:16px;padding:14px 28px}
.app-cta .btn-primary:hover{background:#f1f5f9}

.footer{margin-top:60px;background:var(--card);padding:32px 24px;border-radius:var(--radius);border:1px solid var(--border)}
.footer-inner{display:flex;justify-content:space-between;gap:24px;flex-wrap:wrap;margin-bottom:16px}
.footer-inner strong{color:var(--blue)}
.footer-links{display:flex;gap:14px;flex-wrap:wrap}
.footer-links a{color:var(--slate-light);text-decoration:none;font-size:14px}
.footer-links a:hover{color:var(--blue)}
.footer-source{font-size:13px;color:var(--slate-lighter);border-top:1px solid var(--border);padding-top:16px}
.footer-source a{color:var(--blue);text-decoration:none}

/* AdSense placeholder (will show after approval) */
.ad-slot{margin:24px auto;padding:18px;background:#fafbfc;border:1px dashed var(--border);border-radius:8px;text-align:center;color:var(--slate-lighter);font-size:13px;min-height:90px;display:flex;align-items:center;justify-content:center}
.ad-slot::before{content:"Espacio publicitario"}

@media(max-width:640px){
  .topbar{flex-direction:column;align-items:flex-start}
  .topnav{width:100%}
  h1{font-size:24px}
  .qnav{flex-direction:column}
  .flipcard-front h2{font-size:20px}
  .flipcard-back .answer{font-size:18px}
}
@media print{
  .topbar,.footer,.app-cta,.btn-row,.ad-slot,.qnav,.flipcard-hint{display:none!important}
  body{background:#fff}
  .flipcard{height:auto;min-height:0;page-break-inside:avoid}
  .flipcard-inner{transform:none!important}
  .flipcard-front,.flipcard-back{position:relative;backface-visibility:visible;margin-bottom:14px;border:1px solid #ccc}
  .flipcard-back{transform:none}
  .section,.quiz,.progress-card{box-shadow:none;border:1px solid #ddd}
}