:root {
    --bg-1: #0f1724;
    --bg-2: #0b1220;
    --card: rgba(255, 255, 255, 0.04);
    --glass: rgba(255, 255, 255, 0.06);
    --accent: #7c3aed;
    --accent-2: #06b6d4;
    --btn: rgba(255, 255, 255, 0.06);
    --muted: rgba(255, 255, 255, 0.6);
}

* {
    box-sizing: border-box
}

html,
body {
    height: 100%
}

body {
    margin: 0;
    font-family: Inter, system-ui, -apple-system, "Segoe UI", Roboto, Arial;
    background: linear-gradient(135deg, var(--bg-1), var(--bg-2));
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 24px;
}

.app {
    width: 100%;
    max-width: 420px
}

.calculator {
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.02), rgba(255, 255, 255, 0.01));
    border-radius: 14px;
    padding: 20px;
    box-shadow: 0 8px 30px rgba(2, 6, 23, 0.6);
    border: 1px solid rgba(255, 255, 255, 0.03);
    backdrop-filter: blur(6px);
}

.calc-header h1 {
    margin: 0;
    font-size: 18px;
    color: var(--muted);
    font-weight: 600
}

.display {
    margin-top: 12px
}

#result {
    width: 100%;
    border: 0;
    outline: 0;
    background: transparent;
    color: #fff;
    text-align: right;
    font-size: 32px;
    padding: 12px 14px;
    border-radius: 8px;
}

.buttons {
    margin-top: 14px;
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    align-items: stretch;
}

.btn {
    background: var(--btn);
    color: #fff;
    border: 0;
    padding: 14px 12px;
    border-radius: 10px;
    font-size: 18px;
    cursor: pointer;
    transition: transform .08s ease, box-shadow .08s ease, background .12s;
    box-shadow: 0 2px 6px rgba(2, 6, 23, 0.6);
}

.btn:active {
    transform: translateY(1px) scale(.998)
}

.btn:hover {
    filter: brightness(1.05)
}

.btn-accent {
    background: linear-gradient(90deg, var(--accent), var(--accent-2));
    box-shadow: 0 6px 18px rgba(124, 58, 237, 0.18)
}

.btn-operator {
    background: rgba(255, 255, 255, 0.04);
    color: var(--accent-2)
}

.btn-equal {
    background: var(--accent);
    grid-column: 4/span1;
    grid-row: 4/span2;
    color: #fff;
}

.btn-zero {
    grid-column: 1/span2
}

.btn--spacer {
    background: transparent;
    box-shadow: none;
    visibility: hidden;
    border-radius: 10px
}

@media (max-width:380px) {
    #result {
        font-size: 28px
    }

    .btn {
        padding: 12px;
        font-size: 16px
    }
}