/* ============================================
   CSS Custom Properties — light color palette
   ============================================ */
:root {
    --color-bg: #f0f5ff;
    --color-surface: #ffffff;
    --color-surface-alt: #f5f8fc;
    --color-primary: #4a90d9;
    --color-primary-hover: #3a7bc8;
    --color-text: #2d3748;
    --color-text-light: #718096;
    --color-text-muted: #a0aec0;
    --color-border: #e2e8f0;
    --color-link: #4a90d9;
    --color-error-bg: #fff5f5;
    --color-error-text: #e53e3e;
    --shadow-card: 0 4px 24px rgba(0, 0, 0, 0.06);
    --radius: 12px;
    --container-width: 420px;
    --font-base: 1rem;
}

/* ============================================
   Global reset & layout
   ============================================ */
* { margin: 0; padding: 0; box-sizing: border-box; }

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    font-size: var(--font-base);
    background: var(--color-bg);
    color: var(--color-text);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 1rem;
}

.container {
    background: var(--color-surface);
    border-radius: var(--radius);
    padding: 2rem;
    box-shadow: var(--shadow-card);
    max-width: var(--container-width);
    width: 100%;
}

/* ============================================
   Responsive breakpoints
   ============================================ */

/* Mobile small (< 375px) */
@media (max-width: 374px) {
    :root {
        --container-width: 100%;
        --font-base: 0.875rem;
    }
    .container { padding: 1.25rem; }
}

/* Tablet (768px+) */
@media (min-width: 768px) {
    :root {
        --container-width: 480px;
        --font-base: 1rem;
    }
    .container { padding: 2.5rem; }
}

/* Full HD — 1920px */
@media (min-width: 1920px) {
    :root {
        --container-width: 520px;
        --font-base: 1.05rem;
    }
}

/* 2K — 2560px */
@media (min-width: 2560px) {
    :root {
        --container-width: 580px;
        --font-base: 1.15rem;
    }
    .container { padding: 3rem; }
}

/* 4K — 3840px */
@media (min-width: 3840px) {
    :root {
        --container-width: 720px;
        --font-base: 1.4rem;
    }
    .container {
        padding: 3.5rem;
        border-radius: 20px;
    }
}

/* 5K — 5120px */
@media (min-width: 5120px) {
    :root {
        --container-width: 900px;
        --font-base: 1.7rem;
    }
    .container {
        padding: 4rem;
        border-radius: 24px;
    }
}

/* 6K — 6016px */
@media (min-width: 6016px) {
    :root {
        --container-width: 1080px;
        --font-base: 2rem;
    }
    .container {
        padding: 5rem;
        border-radius: 28px;
    }
}