body {
  font-family: Arial, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;       /* centra horizontal */
  justify-content: center;   /* centra vertical */
  margin: 0;
  min-height: 100vh;
}

.back {
  background: rgb(12, 12, 12);
}

.titulo {
  color: rgb(237, 236, 237);
  margin-bottom: 20px;
  text-align: center;
}

.calculadora {
  border: 2px solid #333;
  padding: 15px;
  width: 240px;
  background: rgb(242, 240, 240);
  border-radius: 12px;
}

#pantalla {
  width: 100%;
  height: 40px;
  margin-bottom: 10px;
  font-size: 18px;
  text-align: right;
  border-radius: 6px;
  border: 1px solid #999;
  padding-right: 5px;
}

.botones {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 6px;
}

button {
  padding: 10px;
  font-size: 16px;
  cursor: pointer;
  border-radius: 8px;
  border: 1px solid #888;
  background-color: #f5f5f5;
}

button:hover {
  background-color: #e0e0e0;
}

.clear {
  grid-column: span 4;
  background-color: #f436ce;
  color: white;
}

.clear:hover {
  background-color: #d32f2f;
}

.btnesp {
  background-color: #0e9ce8;
  color: white;
}

.btn-instrucciones {
  margin-top: 12px;
  padding: 8px;
  background-color: #f44336;
  color: white;
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

.btn-instrucciones:hover {
  background-color: #d32f2f;
}

.instrucciones {
  margin-top: 10px;
  background-color: #222;
  color: white;
  padding: 10px;
  border-radius: 10px;
  font-size: 13px;
}

.oculto {
  display: none;
}

/* HISTORIAL */
.historial {
  margin-top: 12px;
  background-color: #eee;
  border-radius: 10px;
  padding: 10px;
  max-height: 150px;
  overflow-y: auto;
  font-size: 14px;
}

.historial h3 {
  margin: 0 0 6px 0;
  text-align: center;
}

#lista-historial {
  list-style: none;
  padding: 0;
  margin: 0;
}

#lista-historial li {
  padding: 3px 0;
  border-bottom: 1px solid #ccc;
}

.btn-borrar {
  margin-top: 6px;
  width: 100%;
  background-color: #555;
  color: white;
  border: none;
  border-radius: 6px;
}