body {
 margin: 0;
    padding: 0;
    min-height: 100vh;
    display: flex;
    justify-content: center; 
    align-items: center;     
    position: relative;
    
    background: linear-gradient(135deg, #4338ca, #2563eb);
    background-repeat: no-repeat;
    background-attachment: fixed;
  
}


.btn-volver {
position: absolute;
    top: 20px;
    left: 20px;
    padding: 10px 16px;
    background-color: #ffffff;
    color: #1d4ed8;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.15);
}

.btn-volver:hover {
    background-color: #1d4ed8;
    color: #ffffff;
}


.calculadora {
  background-color: #ffffff;
    width: 100%;
    max-width: 320px;
    padding: 22px;
    border-radius: 16px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.25);
    box-sizing: border-box;
    margin: 0;
}


#pantalla {
    width: 100%;
    height: 60px;
    background-color: #f8fafc;
    border: 2px solid #cbd5e1;
    border-radius: 10px;
    font-size: 1.8rem;
    font-weight: bold;
    text-align: right;
    padding: 10px 15px;
    color: #0f172a;
    box-sizing: border-box;
    margin-bottom: 18px;
    outline: none;
}


.botones {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
}


.botones button {
    height: 52px;
    font-size: 1.2rem;
    font-weight: 600;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background-color: #f1f5f9;
    color: #334155;
    transition: all 0.2s ease-in-out;
}

.botones button:hover {
    background-color: #e2e8f0;
    transform: translateY(-2px);
}

.botones button:active {
    transform: translateY(0);
}


.botones .operador, 
.botones #porcentaje {
    background-color: #eff6ff;
    color: #2563eb;
}

.botones .operador:hover, 
.botones #porcentaje:hover {
    background-color: #dbeafe;
}


.botones #borrar {
    background-color: #fef2f2;
    color: #ef4444;
}

.botones #borrar:hover {
    background-color: #fee2e2;
}


.botones #igual {
    background-color: #1d4ed8;
    color: #ffffff;
}

.botones #igual:hover {
    background-color: #1e40af;
}