body {
    font-family: 'Montserrat', sans-serif;
    background: #0f172a;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    color: #e5e7eb;
}

.container {
    width: 320px;
    background: #020617;
    border-radius: 14px;
    box-shadow: 0 15px 40px rgba(0,0,0,0.6);
    padding: 15px;
}

.header {
    text-align: center;
    font-size: 24px;
    font-weight: 600;
    color: #f8fafc;
    margin-bottom: 15px;
    letter-spacing: 1px;
}

#display {
    width: 100%;
    height: 60px;
    font-size: 26px;
    text-align: right;
    padding: 10px;
    border-radius: 10px;
    border: none;
    background: #020617;
    color: #f8fafc;
    margin-bottom: 15px;
    box-sizing: border-box;
    box-shadow: inset 0 0 0 1px #1e293b;
}

#display::placeholder {
    color: #64748b;
}

.row {
    display: flex;
}

button {
    flex: 1;
    margin: 6px;
    height: 55px;
    font-size: 20px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background: #1e293b;
    color: #e5e7eb;
    transition: all 0.2s ease;
}

button:hover {
    background: #334155;
}

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

/* Operators */
.operator {
    background: #7c3aed;
}

.operator:hover {
    background: #6d28d9;
}

/* Clear */
.clear {
    background: #dc2626;
}

.clear:hover {
    background: #b91c1c;
}

/* Equal */
.equal {
    background: #16a34a;
}

.equal:hover {
    background: #15803d;
}