:root {
    --bg: #111827;
    --card: #0b1220;
    --muted: #9aa4b2;
    --accent: #2adb16;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: system-ui, -apple-system, Segoe UI, Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: linear-gradient(
        135deg,
        #111827 0%,
        #1e293b 50%,
        #0f172a 100%
    );
    color: #f8fafc;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

header {
    padding: 1rem 1.25rem;
    border-bottom: 1px solid rgba(255, 255, 255, 0.03);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.brand {
    display: flex;
    gap: 0.75rem;
    align-items: center;
}

.logo {
    width: 40px;
    height: 40px;
    border-radius: 8px;
    background: linear-gradient(135deg, var(--accent), #7c3aed);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    color: white;
}

nav a {
    color: var(--muted);
    text-decoration: none;
    margin-left: 1rem;
    font-size: 0.95rem;
}

main {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 2rem;
}

.card {
    width: 100%;
    max-width: 900px;
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.02), transparent);
    border: 1px solid rgba(255, 255, 255, 0.04);
    padding: 2rem;
    border-radius: 12px;
}

h1 {
    margin: 0 0 0.5rem 0;
    font-size: 1.75rem;
}

p.lead {
    color: var(--muted);
    margin: 0 0 1.25rem 0;
}

.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 1rem;
}

.item {
    background: rgba(255, 255, 255, 0.02);
    padding: 1rem;
    border-radius: 8px;
}

.input-number {
    padding: .5rem;
    border-radius: 6px;
    border: 1px solid var(--muted);
    width: 100%;
    max-width: 200px;
    background: transparent;
    color: inherit;
}
.input-number.invalid {
    border-color: #ff6b6b;
    box-shadow: 0 0 0 4px rgba(255,107,107,0.06);
}
.error-text {
    color: #ffb4b4;
    font-size: 0.9rem;
    margin-top: .45rem;
    display: block;
}

.input-row {
    display: flex;
    gap: .5rem;
    align-items: center;
}
.btn {
    appearance: none;
    border: none;
    background: linear-gradient(180deg, var(--accent), #16a34a);
    color: #062017;
    padding: .5rem .75rem;
    border-radius: 8px;
    font-weight: 600;
    cursor: pointer;
}
.btn[disabled] {
    opacity: .5;
    cursor: not-allowed;
}
.confirm-icon {
    width: 20px;
    height: 20px;
    display: inline-block;
    color: var(--accent);
    opacity: 0;
    transition: opacity .15s ease;
}
.confirm-icon.visible {
    opacity: 1;
}

footer {
    padding: 1rem 1.25rem;
    border-top: 1px solid rgba(255, 255, 255, 0.03);
    text-align: center;
    color: var(--muted);
    font-size: 0.9rem;
}

@media (max-width: 520px) {
    h1 {
        font-size: 1.25rem;
    }

    .logo {
        width: 36px;
        height: 36px;
    }
}