* {
    box-sizing: border-box;
}

body {
    font-family: "Segoe UI", Tahoma, sans-serif;
    background: linear-gradient(135deg, #020617, #0f172a);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    color: #fff;
}

.calculator {
    background: #020617;
    padding: 28px;
    width: 340px;
    border-radius: 18px;
    box-shadow: 0 25px 50px rgba(0,0,0,0.8);
}

h2 {
    text-align: center;
    margin-bottom: 18px;
    color: #38bdf8;
}

#display {
    width: 100%;
    height: 60px;
    background: #020617;
    border: 1px solid #1e293b;
    border-radius: 12px;
    color: #fff;
    font-size: 24px;
    padding: 10px;
    text-align: right;
    margin-bottom: 20px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

button {
    padding: 14px;
    border-radius: 12px;
    border: none;
    font-size: 16px;
    cursor: pointer;
    background: #020617;
    color: #fff;
    border: 1px solid #1e293b;
    transition: 0.2s;
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 14px rgba(255,255,255,0.08);
}

.op {
    color: #38bdf8;
    font-weight: bold;
}

.equal {
    background: linear-gradient(135deg, #22c55e, #16a34a);
    color: #022c22;
    font-weight: bold;
}

.zero {
    grid-column: span 2;
}