* {
    box-sizing: border-box;
    font-family: Arial, sans-serif;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #f0f2f5;
    margin: 0;
}

.contenedor-principal {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 15px;
}

.btn-regresar {
    display: inline-block;
    padding: 10px 20px;
    background-color: #007bff;
    color: white;
    text-decoration: none;
    border-radius: 6px;
    font-weight: bold;
    font-size: 14px;
    transition: background-color 0.2s;
}

.btn-regresar:hover {
    background-color: #0056b3;
}

.calculadora {
    background-color: #ffffff;
    padding: 20px;
    border-radius: 12px;
    box-shadow: 0px 4px 10px rgba(0, 0, 0, 0.15);
    width: 300px;
}

#pantalla {
    width: 100%;
    height: 50px;
    font-size: 24px;
    text-align: right;
    padding: 10px;
    margin-bottom: 15px;
    border: 1px solid #ccc;
    border-radius: 6px;
    background-color: #eaeff2;
    color: #333;
}

.botones {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

button {
    height: 45px;
    font-size: 18px;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    background-color: #e0e0e0;
    transition: background-color 0.2s;
}

button:hover {
    background-color: #d0d0d0;
}

.operador {
    background-color: #ff9800;
    color: white;
}

.operador:hover {
    background-color: #e68a00;
}

#borrar {
    background-color: #f44336;
    color: white;
}

#borrar:hover {
    background-color: #d32f2f;
}

.igual {
    background-color: #4caf50;
    color: white;
    grid-row: span 2;
    height: 100%;
}

.igual:hover {
    background-color: #388e3c;
}

.cero {
    grid-column: span 2;
}

.punto {
    background-color: #e0e0e0;
    font-weight: bold;
}