:root{
  --tinta:#1c2333; --papel:#f7f8fb; --caja:#ffffff; --borde:#d7dce6;
  --acento:#1c5d99; --acento2:#0d7a5f; --mal:#a8322d; --bien:#0d7a5f;
  --suave:#eef2f8; --gris:#5d6675;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  background:var(--papel); color:var(--tinta);
  font-family:"Segoe UI",system-ui,-apple-system,sans-serif;
  font-size:17px; line-height:1.6; overflow-x:hidden;
}
header{background:var(--tinta); color:#fff; padding:1rem 1rem .6rem}
.volver-sitio{display:inline-block; color:#b9c3d6; text-decoration:none; font-size:.8rem; margin-bottom:.35rem}
.volver-sitio:hover{color:#fff; text-decoration:underline}
header h1{font-size:1.15rem; margin:0 0 .2rem; font-weight:600; letter-spacing:.2px}
header p{margin:0; font-size:.82rem; color:#b9c3d6}

#barra-estado{position:sticky; top:0; z-index:50; background:var(--tinta); padding:.5rem 1rem .7rem; color:#fff}
.progreso-riel{height:8px; background:#3a445c; border-radius:6px; overflow:hidden}
.progreso-lleno{height:100%; width:0%; background:linear-gradient(90deg,#3f9ae0,#59d0a8); transition:width .35s}
.estado-txt{display:flex; justify-content:space-between; font-size:.78rem; margin-top:.35rem; color:#c9d3e5}

nav#secciones{position:sticky; top:0; z-index:49; display:flex; gap:.4rem; overflow-x:auto;
  padding:.55rem 1rem; background:#e7ecf5; border-bottom:1px solid var(--borde);
  -webkit-overflow-scrolling:touch}
nav#secciones button{flex:0 0 auto; border:1px solid var(--borde); background:#fff; color:var(--tinta);
  border-radius:999px; padding:.35rem .8rem; font-size:.8rem; cursor:pointer; font-family:inherit}
nav#secciones button.activa{background:var(--acento); color:#fff; border-color:var(--acento)}

main{padding:1rem; max-width:820px; margin:0 auto}
section.pantalla{display:none}
section.pantalla.visible{display:block}

.rotulo{display:inline-block; font-size:.72rem; letter-spacing:.6px; text-transform:uppercase;
  background:var(--suave); border:1px solid var(--borde); color:var(--gris);
  padding:.2rem .6rem; border-radius:4px; margin-bottom:.6rem}
h2{font-size:1.25rem; margin:.2rem 0 .8rem; scroll-margin-top:var(--tope,140px)}
h3{font-size:1rem; margin:1.2rem 0 .4rem; color:var(--acento); scroll-margin-top:var(--tope,140px)}

.caja{background:var(--caja); border:1px solid var(--borde); border-radius:10px; padding:.9rem; margin:.8rem 0}
.caja.idea{border-left:4px solid var(--acento)}
.caja.aviso{border-left:4px solid var(--mal); background:#fdf4f3}
.caja.limite{border-left:4px solid var(--acento2); background:#f2faf7}
.caja h4{margin:0 0 .35rem; font-size:.92rem; text-transform:uppercase; letter-spacing:.4px; color:var(--gris)}

ul.rapida{margin:.3rem 0 .3rem 1.1rem; padding:0}
ul.rapida li{margin:.22rem 0}

.jxgbox{width:100%; height:340px; border:1px solid var(--borde); border-radius:8px; background:#fff; touch-action:none}
.controles{display:grid; grid-template-columns:1fr; gap:.45rem; margin:.7rem 0}
.cartel{background:var(--suave); border:1px solid var(--borde); border-radius:8px; padding:.7rem; margin-top:.6rem; font-size:.95rem}
.cartel.unica{border-left:4px solid var(--bien)}
.cartel.ninguna{border-left:4px solid var(--mal)}
.cartel.infinitas{border-left:4px solid var(--acento)}
.ecuaciones{display:flex; flex-wrap:wrap; gap:.9rem; margin:.5rem 0; font-size:1rem}

.item{scroll-margin-top:var(--tope,140px); background:var(--caja); border:1px solid var(--borde); border-radius:10px; padding:.9rem; margin:1rem 0}
.item .cab{display:flex; justify-content:space-between; align-items:center; gap:.5rem; margin-bottom:.5rem}
.item .cod{font-size:.72rem; font-weight:700; letter-spacing:.5px; color:var(--gris)}
.item .pts{font-size:.72rem; background:var(--suave); border-radius:999px; padding:.15rem .55rem; color:var(--gris)}
.consigna{margin:.2rem 0 .6rem}
.opciones{display:flex; flex-direction:column; gap:.45rem}
.opciones button{width:100%; text-align:left; font-family:inherit; font-size:.95rem; line-height:1.45;
  background:#fff; border:1px solid var(--borde); border-radius:8px; padding:.6rem .7rem; cursor:pointer; color:inherit}
.opciones button:active{background:var(--suave)}
.opciones button[disabled]{cursor:default; opacity:1}
.opciones button.correcta{border-color:var(--bien); background:#eaf7f2}
.opciones button.elegida-mal{border-color:var(--mal); background:#fdeceb}
.devolucion{margin-top:.6rem; font-size:.9rem; border-radius:8px; padding:.6rem .7rem}
.devolucion.ok{background:#eaf7f2; border:1px solid #9dd3bf}
.devolucion.no{background:#fdeceb; border:1px solid #e2b1ad}
.devolucion .etiqueta{font-weight:700; display:block; margin-bottom:.2rem}
.autoverif{font-size:.85rem; color:var(--gris); margin-top:.5rem; font-style:italic}
.volver-teoria{margin-top:.6rem; font-size:.85rem; background:none; border:none; color:var(--acento);
  text-decoration:underline; padding:0; cursor:pointer; font-family:inherit}

table.tabla{border-collapse:collapse; width:100%; font-size:.92rem; margin:.5rem 0}
table.tabla th,table.tabla td{border:1px solid var(--borde); padding:.35rem .4rem; text-align:center}
table.tabla th{background:var(--suave); font-weight:600}
table.tabla input{width:100%; min-width:3.2rem; border:1px solid var(--borde); border-radius:5px;
  padding:.3rem; font-size:.95rem; text-align:center; font-family:inherit}
table.tabla input.ok{border-color:var(--bien); background:#eaf7f2}
table.tabla input.no{border-color:var(--mal); background:#fdeceb}
.tabla-envoltorio{overflow-x:auto}

video{width:100%; border-radius:10px; border:1px solid var(--borde); background:#000}
.mal-resuelto{background:#fbfbfd; border:1px dashed var(--borde); border-radius:8px; padding:.7rem; margin:.5rem 0; font-size:.95rem}
.mal-resuelto ol{margin:.2rem 0 0 1.1rem; padding:0}
.mal-resuelto li{margin:.3rem 0}

.btn{background:var(--acento); color:#fff; border:none; border-radius:8px; padding:.6rem 1rem;
  font-size:.95rem; font-family:inherit; cursor:pointer}
.btn.sec{background:#fff; color:var(--acento); border:1px solid var(--acento)}
.pie-nav{display:flex; gap:.5rem; justify-content:space-between; margin:1.4rem 0 2rem}
.cierre-nivel{border-left:4px solid var(--acento); background:#fff; border:1px solid var(--borde);
  border-radius:10px; padding:.9rem; margin:.8rem 0}
footer{padding:1.2rem 1rem 2.5rem; text-align:center; font-size:.78rem; color:var(--gris)}
@media (min-width:640px){ .controles{grid-template-columns:1fr 1fr} }

/* ---- Problemas ABP: consigna abierta y resultado plegado ---- */
.item.abp{border-left:4px solid var(--acento2)}
.item.abp .consigna{font-size:1rem}
details.resultado{margin-top:.7rem; border:1px solid var(--borde); border-radius:8px; background:var(--suave)}
details.resultado summary{cursor:pointer; padding:.55rem .7rem; font-size:.9rem; font-weight:600;
  color:var(--acento); list-style:none}
details.resultado summary::-webkit-details-marker{display:none}
details.resultado summary::before{content:"▸ "; font-weight:400}
details.resultado[open] summary::before{content:"▾ "}
details.resultado[open] summary{border-bottom:1px solid var(--borde)}
details.resultado p{margin:0; padding:.6rem .7rem; font-size:.95rem}