/* ==========================================================================
   Logic Typing Tutor — Shared Design System (2026)
   ========================================================================== */

:root {
    /* Color palette */
    --color-ink: #07151c;
    --color-navy: #0b202a;
    --color-deep-teal: #103944;
    --color-teal: #1d7482;
    --color-bright-teal: #35b8c8;
    --color-teal-hover: #1b8f9e;
    --color-teal-light: #4bd4e3;
    --color-ice: #f4f8f9;
    --color-ice-dark: #e8f0f2;
    --color-steel: #9fb1b8;
    --color-white: #ffffff;
    --color-body: #263238;
    --color-muted: #526a72;
    --color-muted-dark: #38545d;
    --color-on-dark: #c4d2d7;
    --color-on-dark-muted: #d7eef2;
    --color-warning-bg: #fff7df;
    --color-warning-border: #ffc107;
    --color-warning-text: #765600;
    --color-warning-strong: #4d3800;

    /* Typography */
    --font-family: "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, "Helvetica Neue", Arial, sans-serif;
    --font-size-xs: 0.8125rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-md: 1.0625rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.5rem;
    --font-size-2xl: 2.25rem;
    --line-height-tight: 1.15;
    --line-height-base: 1.6;
    --line-height-relaxed: 1.85;
    --letter-spacing-tight: -0.025em;
    --letter-spacing-wide: 0.05em;

    /* Spacing scale */
    --space-1: 0.25rem;
    --space-2: 0.5rem;
    --space-3: 0.75rem;
    --space-4: 1rem;
    --space-5: 1.25rem;
    --space-6: 1.5rem;
    --space-8: 2rem;
    --space-10: 2.5rem;
    --space-12: 3rem;
    --space-16: 4rem;
    --space-20: 5.25rem;

    /* Layout */
    --container-max: 75rem;
    --container-narrow: 57.5rem;
    --header-sticky-offset: 6rem;
    --sidebar-sticky-top: 1.25rem;

    /* Radii */
    --radius-sm: 0.5rem;
    --radius-md: 0.875rem;
    --radius-lg: 1.125rem;
    --radius-pill: 999px;

    /* Shadows */
    --shadow-sm: 0 0.625rem 1.75rem rgba(7, 21, 28, 0.08);
    --shadow-md: 0 0.875rem 2.125rem rgba(7, 21, 28, 0.12);
    --shadow-lg: 0 1.125rem 2.8125rem rgba(7, 21, 28, 0.18);
    --shadow-cta: 0 1.125rem 2.8125rem rgba(7, 21, 28, 0.48);

    /* Motion */
    --ease-out: cubic-bezier(0.22, 1, 0.36, 1);
    --duration-fast: 150ms;
    --duration-base: 300ms;
    --duration-slow: 400ms;

    /* Focus ring */
    --focus-ring: 0 0 0 3px var(--color-white), 0 0 0 5px var(--color-bright-teal);
}

/* Reset */
*,
*::before,
*::after {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    -webkit-text-size-adjust: 100%;
}

body {
    margin: 0;
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: var(--line-height-base);
    color: var(--color-ink);
    background: linear-gradient(180deg, var(--color-ice) 0%, var(--color-ice-dark) 100%);
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

/* Skip link — WCAG 2.4.1 */
.skip-link {
    position: absolute;
    top: -100%;
    left: var(--space-4);
    z-index: 10000;
    padding: var(--space-3) var(--space-5);
    background: var(--color-navy);
    color: var(--color-white);
    text-decoration: none;
    border-radius: var(--radius-sm);
    font-weight: 700;
}

.skip-link:focus {
    top: var(--space-4);
    outline: none;
    box-shadow: var(--focus-ring);
}

/* Global focus — WCAG 2.4.7 */
:focus {
    outline: none;
}

:focus-visible {
    outline: 2px solid var(--color-bright-teal);
    outline-offset: 3px;
}

a {
    color: inherit;
}

/* Shared utilities */
.container {
    width: min(100%, var(--container-max));
    margin-inline: auto;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

.section-heading {
    font-size: clamp(1.625rem, 3vw, var(--font-size-2xl));
    color: var(--color-navy);
    margin-bottom: var(--space-5);
    font-weight: 800;
    position: relative;
    display: inline-block;
    letter-spacing: var(--letter-spacing-tight);
}

.section-heading::after {
    content: "";
    position: absolute;
    width: 4.25rem;
    height: 4px;
    background: linear-gradient(90deg, var(--color-bright-teal), var(--color-teal));
    bottom: -0.75rem;
    left: 50%;
    transform: translateX(-50%);
    border-radius: var(--radius-pill);
}

/* Shared CTA button */
.btn-download {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-3);
    background: linear-gradient(135deg, var(--color-bright-teal), var(--color-teal));
    color: var(--color-white);
    text-decoration: none;
    font-size: var(--font-size-lg);
    padding: 1.25rem 2.75rem;
    width: min(92%, 32.5rem);
    border: 1px solid rgba(255, 255, 255, 0.58);
    border-radius: var(--radius-pill);
    font-weight: 800;
    letter-spacing: 0.0125em;
    box-shadow: var(--shadow-cta), 0 0 0 8px rgba(255, 255, 255, 0.12);
    transition:
        transform var(--duration-base) var(--ease-out),
        box-shadow var(--duration-base) var(--ease-out),
        background var(--duration-base) var(--ease-out);
}

.btn-download:hover {
    background: linear-gradient(135deg, var(--color-teal-light), var(--color-teal-hover));
    box-shadow: 0 1.375rem 3.4375rem rgba(7, 21, 28, 0.58), 0 0 0 10px rgba(255, 255, 255, 0.16);
    transform: translateY(-3px);
}

.btn-download:focus-visible {
    box-shadow: var(--focus-ring), var(--shadow-cta);
}

/* Reduced motion — WCAG 2.3.3 */
@media (prefers-reduced-motion: reduce) {
    html {
        scroll-behavior: auto;
    }

    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}