:root {
        --bg: #0f172a;
        --card: rgba(255, 255, 255, 0.08);
        --border: rgba(255, 255, 255, 0.15);
        --text: #e5e7eb;
        --muted: #94a3b8;
        --accent: #6366f1;
        --danger: #ef4444;
    }

    * {
        box-sizing: border-box;
        font-family: "Inter", system-ui, sans-serif;
    }

    body {
        margin: 0;
        height: 100vh;
        background: radial-gradient(circle at top, #1e293b, #020617);
        display: flex;
        align-items: center;
        justify-content: center;
        color: var(--text);
    }

    .calculator {
        width: 360px;
        background: var(--card);
        backdrop-filter: blur(16px);
        border: 1px solid var(--border);
        border-radius: 20px;
        padding: 20px;
        box-shadow: 0 20px 40px rgba(0,0,0,0.4);
    }

    .display {
        background: rgba(0,0,0,0.4);
        border-radius: 14px;
        padding: 18px;
        text-align: right;
        overflow: hidden;
    }

    .expression {
        font-size: 14px;
        color: var(--muted);
        min-height: 18px;
    }

    .result {
        font-size: 32px;
        font-weight: 600;
        margin-top: 6px;
        word-break: break-all;
    }

    .buttons {
        margin-top: 20px;
        display: grid;
        grid-template-columns: repeat(4, 1fr);
        gap: 12px;
    }

    button {
        height: 58px;
        border-radius: 14px;
        border: none;
        background: rgba(255,255,255,0.08);
        color: var(--text);
        font-size: 18px;
        cursor: pointer;
        transition: all 0.15s ease;
    }

    button:hover {
        background: rgba(255,255,255,0.15);
    }

    button:active {
        transform: scale(0.96);
    }

    .operator {
        color: #a5b4fc;
    }

    .accent {
        background: var(--accent);
        color: white;
    }

    .accent:hover {
        background: #4f46e5;
    }

    .danger {
        color: var(--danger);
    }

    .span-2 {
        grid-column: span 2;
    }

    @media (max-width: 420px) {
        .calculator {
            width: 92%;
        }
    }