* {
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    height: 100vh;
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    background: linear-gradient(135deg, #667eea, #764ba2);
}

#app {
    background: linear-gradient(135deg, #ffffff, #f0f0f0);
    /* colore base */
    transition: background 0.3s;
    padding: 40px;
    border-radius: 16px;
    text-align: center;
    width: 320px;
    box-shadow: 0 15px 40px rgba(0, 0, 0, 0.25);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
}

#app h1 {
    font-size: 72px;
    margin: 0;
    color: #333;
    transition: transform 0.2s, color 0.2s;
}

#app button {
    font-size: 28px;
    min-width: 70px;
    height: 70px;
    margin: 0 10px;
    border: none;
    border-radius: 50%;
    cursor: pointer;
    background: #667eea;
    color: white;
    transition: transform 0.2s, background 0.2s;
    padding: 15px;

}

#app button:hover {
    background: #5a67d8;
    transform: scale(1.1);
    box-shadow: 0 0 15px rgba(255, 255, 255, 0.4);
}

#app button:active {
    transform: scale(0.95);
}

/* Stile specifico per RESET */
#app button:last-child {
    background: #e53e3e;
}

#app button:last-child:hover {
    background: #c53030;
}

#app button:last-child:active {
    transform: scale(0.95);
    background: #d53e3e;
    /* un rosso un po' più scuro quando premi */
}

.counter-positive {
    color: #38a169;
}


.counter-negative {
    color: #e53e3e;
}

.counter-zero {
    color: #333;
}

#app button span {
    display: inline-block;
    position: relative;
    top: -3px;

}