* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Poppins', sans-serif;
}

body {
    background: radial-gradient(circle at top, #1e293b, #020617);
    min-height: 100vh;
}

/* Main wrapper */
.container {
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

/* Calculator card */
.calculator {
    background: #0f172a;
    padding: 22px;
    border-radius: 18px;
    box-shadow: 0 20px 45px rgba(0, 0, 0, 0.6);
    width: 320px; /* PC size fixed */
}

/* Display */
.display {
    margin-bottom: 18px;
}

.display input {
    width: 100%;
    height: 70px;
    border-radius: 12px;
    background: #020617;
    color: #e5e7eb;
    font-size: 36px;
    text-align: right;
    padding: 0 14px;
    border: none;
    outline: none;
}

/* Buttons */
.calculator form div {
    display: flex;
    justify-content: space-between;
}

.calculator form input[type="button"] {
    width: 65px;
    height: 60px;
    margin: 6px;
    border-radius: 14px;
    border: none;
    font-size: 18px;
    cursor: pointer;
    background: #1e293b;
    color: #f8fafc;
    box-shadow: inset 2px 2px 4px rgba(255,255,255,0.05),
                inset -2px -2px 6px rgba(0,0,0,0.6);
    transition: all 0.2s ease;
}

.calculator form input[type="button"]:hover {
    background: #334155;
}

/* Operators */
.operator {
    color: #38bdf8;
    background: #020617;
}

/* Equal button */
.equal {
    width: 142px;
    background: linear-gradient(135deg, #38bdf8, #2563eb);
    color: #020617;
    font-weight: 600;
}

.equal:hover {
    opacity: 0.9;
}

/* Mobile responsiveness */
@media (max-width: 420px) {
    .calculator {
        width: 100%;
        max-width: 340px;
    }

    .container {
        align-items: flex-start;
        padding-top: 40px;
    }
}