:root {
  --fondo: #f0f0f0;
  --panel: #ffffff;
  --texto: #000;
}

body.oscuro {
  --fondo: #1e1e1e;
  --panel: #2c2c2c;
  --texto: #ffffff;
}

body {
  background: var(--fondo);
  color: var(--texto);
  font-family: Arial, sans-serif;
  padding: 20px;
}

.menu-btn, .tema-btn {
  position: fixed;
  top: 20px;
  padding: 10px;
  font-size: 18px;
  cursor: pointer;
}

.menu-btn { left: 20px; }
.tema-btn { right: 20px; }

.contenedor {
  display: flex;
  justify-content: center;
}

.calculadora {
  background: var(--panel);
  padding: 20px;
  width: 260px;
  border-radius: 10px;
}

input {
  width: 90%;
  margin: 0 auto 10px auto;
  padding: 8px;
  display: block;
  text-align: center;
  font-size: 16px;
}


.botones {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 5px;
}

.botones button {
  padding: 10px;
  font-size: 18px;
}

.historial {
  position: fixed;
  right: -260px;
  top: 0;
  width: 250px;
  height: 100%;
  background: var(--panel);
  padding: 10px;
  overflow-y: auto;
  transition: right 0.3s;
}

.historial.activo {
  right: 0;
}

.historial ul {
  list-style: none;
  padding: 0;
}

.historial li {
  background: #9993;
  margin: 5px 0;
  padding: 5px;
  border-radius: 5px;
  font-size: 14px;
}

.firma {
  margin-top: 15px;
  text-align: center;
  font-size: 12px;
  opacity: 0.6;
}