body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%); 
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.calcolatrice {
    background: #ecf0f1;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
    width: 300px;
}

#display {
    width: 100%;
    padding: 15px;
    font-size: 1.5rem;
    text-align: right;
    margin-bottom: 10px;
    border: 2px solid #bdc3c7;
    border-radius: 5px;
    box-sizing: border-box; /* Importante per il padding */
}

#messaggio-errore {
    color: red;
    font-size: 0.8rem;
    text-align: center;
    margin-bottom: 10px;
    height: 20px; /* Per non far saltare il layout */
}

.nascosto {
    visibility: hidden; /* Nasconde ma tiene lo spazio */
}

.tastiera {
    display: grid;
    grid-template-columns: repeat(4, 1fr); /* 4 colonne uguali */
    gap: 10px;
}

.tasto {
    padding: 20px;
    font-size: 1.2rem;
    border: none;
    background: white;
    border-radius: 5px;
    cursor: pointer;
    transition: 0.2s;
}

.tasto:hover {
    background-color: #dfe6e9;
}

.tasto.op {
    background-color: #f39c12;
    color: white;
}

.tasto.op:hover {
    background-color: #e67e22;
}

#btn-uguale {
    background-color: #27ae60;
    color: white;
}

#btn-cancella {
    background-color: #c0392b;
    color: white;
}