/* ==========================================================
   Variables
   ========================================================== */
:root {
  /* Colors */
  --color-bg: #f7fafc;            /* soft white */
  --color-surface: #ffffff;       /* card / panels */
  --color-text: #111827;          /* near-black for strong legibility */
  --color-text-muted: #6b7280;    /* cool gray */
  --color-primary: #2563eb;       /* light / mid blue */
  --color-primary-soft: #e0edff;  /* subtle primary tint */
  --color-accent-navy: #0f172a;   /* navy accents */
  --color-accent-green: #10b981;  /* subtle green highlight */
  --color-border-subtle: #e5e7eb; /* light gray border */
  --color-border-strong: #9ca3af; /* stronger gray border */

  --color-success: #16a34a;
  --color-warning: #f59e0b;
  --color-danger: #dc2626;

  --color-neutral-50: #f9fafb;
  --color-neutral-100: #f3f4f6;
  --color-neutral-200: #e5e7eb;
  --color-neutral-300: #d1d5db;
  --color-neutral-400: #9ca3af;
  --color-neutral-500: #6b7280;
  --color-neutral-600: #4b5563;
  --color-neutral-700: #374151;
  --color-neutral-800: #1f2933;
  --color-neutral-900: #111827;

  /* Typography */
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "SF Pro Text",
    "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-mono: "SF Mono", Menlo, Monaco, Consolas, "Liberation Mono",
    "Courier New", monospace;

  --font-size-xs: 0.75rem;   /* 12px */
  --font-size-sm: 0.875rem;  /* 14px */
  --font-size-base: 1rem;    /* 16px */
  --font-size-lg: 1.125rem;  /* 18px */
  --font-size-xl: 1.25rem;   /* 20px */
  --font-size-2xl: 1.5rem;   /* 24px */
  --font-size-3xl: 1.875rem; /* 30px */
  --font-size-4xl: 2.25rem;  /* 36px */

  --line-height-tight: 1.15;
  --line-height-snug: 1.3;
  --line-height-normal: 1.5;
  --line-height-relaxed: 1.7;

  /* Spacing scale (px values) */
  --space-0: 0;
  --space-1: 0.25rem;  /* 4px */
  --space-2: 0.5rem;   /* 8px */
  --space-3: 0.75rem;  /* 12px */
  --space-4: 1rem;     /* 16px */
  --space-5: 1.25rem;  /* 20px */
  --space-6: 1.5rem;   /* 24px */
  --space-8: 2rem;     /* 32px */
  --space-10: 2.5rem;  /* 40px */
  --space-12: 3rem;    /* 48px */
  --space-16: 4rem;    /* 64px */
  --space-20: 5rem;    /* 80px */
  --space-24: 6rem;    /* 96px */

  /* Radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-full: 9999px;

  /* Shadows (soft, minimal) */
  --shadow-xs: 0 1px 2px rgba(15, 23, 42, 0.04);
  --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.08);
  --shadow-md: 0 4px 16px rgba(15, 23, 42, 0.08);

  /* Transitions */
  --transition-fast: 120ms ease-out;
  --transition-base: 180ms ease-out;
  --transition-slow: 240ms ease-out;
}

/* Respect reduced motion preferences */
@media (prefers-reduced-motion: reduce) {
  :root {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
}

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

html,
body {
  margin: 0;
  padding: 0;
}

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

body {
  min-height: 100vh;
}

img,
picture,
video,
canvas,
svg {
  display: block;
  max-width: 100%;
}

img {
  height: auto;
}

input,
button,
textarea,
select {
  font: inherit;
  color: inherit;
}

button {
  border: none;
  padding: 0;
  background: none;
}

ul,
ol {
  list-style: none;
  margin: 0;
  padding: 0;
}

h1,
h2,
h3,
h4,
h5,
h6,
p,
figure,
blockquote,
dl,
dd {
  margin: 0;
}

/* ==========================================================
   Base Styles
   ========================================================== */
body {
  font-family: var(--font-sans);
  font-size: var(--font-size-base);
  line-height: var(--line-height-normal);
  color: var(--color-text);
  background-color: var(--color-bg);
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

main {
  display: block;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-weight: 600;
  color: var(--color-accent-navy);
  line-height: var(--line-height-snug);
}

h1 {
  font-size: clamp(2.25rem, 2.1rem + 1vw, 3rem);
  letter-spacing: -0.04em;
  margin-bottom: var(--space-4);
}

h2 {
  font-size: clamp(1.875rem, 1.7rem + 0.5vw, 2.25rem);
  letter-spacing: -0.03em;
  margin-bottom: var(--space-3);
}

h3 {
  font-size: var(--font-size-2xl);
  letter-spacing: -0.02em;
  margin-bottom: var(--space-2);
}

h4 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--space-2);
}

h5 {
  font-size: var(--font-size-lg);
  margin-bottom: var(--space-1);
}

h6 {
  font-size: var(--font-size-base);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-text-muted);
  margin-bottom: var(--space-1);
}

p {
  margin-bottom: var(--space-4);
  color: var(--color-text-muted);
}

strong {
  font-weight: 600;
  color: var(--color-accent-navy);
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-base);
}

a:hover {
  color: var(--color-accent-navy);
}

a:focus-visible {
  outline: 2px solid var(--color-accent-green);
  outline-offset: 2px;
}

code,
pre {
  font-family: var(--font-mono);
}

pre {
  margin: 0;
}

/* ==========================================================
   Accessibility & Focus
   ========================================================== */
:focus-visible {
  outline: 2px solid var(--color-accent-green);
  outline-offset: 2px;
}

:focus {
  outline: none;
}

/* Screen reader only utility */
.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;
}

.sr-only-focusable:active,
.sr-only-focusable:focus {
  position: static;
  width: auto;
  height: auto;
  margin: 0;
  overflow: visible;
  clip: auto;
  white-space: normal;
}

/* ==========================================================
   Layout Utilities
   ========================================================== */
/* Centered content with max-width tuned for reading and grid visuals */
.container {
  width: 100%;
  margin-left: auto;
  margin-right: auto;
  padding-left: var(--space-4);
  padding-right: var(--space-4);
  max-width: 1120px;
}

@media (min-width: 768px) {
  .container {
    padding-left: var(--space-6);
    padding-right: var(--space-6);
  }
}

.section {
  padding-top: var(--space-12);
  padding-bottom: var(--space-12);
}

.section--tight {
  padding-top: var(--space-8);
  padding-bottom: var(--space-8);
}

/* Flex helpers */
.flex {
  display: flex;
}

.inline-flex {
  display: inline-flex;
}

.flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

.flex-between {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.flex-column {
  display: flex;
  flex-direction: column;
}

.flex-wrap {
  flex-wrap: wrap;
}

.gap-xs {
  gap: var(--space-2);
}

.gap-sm {
  gap: var(--space-3);
}

.gap-md {
  gap: var(--space-4);
}

.gap-lg {
  gap: var(--space-6);
}

/* Grid helpers - encourage structured, puzzle-like layout */
.grid {
  display: grid;
}

.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-6);
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-6);
}

@media (max-width: 768px) {
  .grid-2,
  .grid-3 {
    grid-template-columns: minmax(0, 1fr);
  }
}

/* Simple utility spacing (limited to keep base lightweight) */
.mt-0 {
  margin-top: 0 !important;
}

.mt-sm {
  margin-top: var(--space-3) !important;
}

.mt-md {
  margin-top: var(--space-4) !important;
}

.mt-lg {
  margin-top: var(--space-6) !important;
}

.mb-0 {
  margin-bottom: 0 !important;
}

.mb-sm {
  margin-bottom: var(--space-3) !important;
}

.mb-md {
  margin-bottom: var(--space-4) !important;
}

.mb-lg {
  margin-bottom: var(--space-6) !important;
}

.text-center {
  text-align: center !important;
}

.text-right {
  text-align: right !important;
}

/* ==========================================================
   Components
   ========================================================== */
/* Buttons - clean, minimal, focus on clarity and intent */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: 0.6rem 1.25rem;
  border-radius: var(--radius-full);
  font-size: var(--font-size-sm);
  font-weight: 500;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  border: 1px solid transparent;
  cursor: pointer;
  transition:
    background-color var(--transition-base),
    color var(--transition-base),
    box-shadow var(--transition-base),
    border-color var(--transition-base),
    transform var(--transition-fast);
}

.btn--primary {
  background: linear-gradient(135deg, #2563eb, #1d4ed8);
  color: #ffffff!important;
  box-shadow: var(--shadow-sm);
}

.btn--primary:hover {
  background: linear-gradient(135deg, #1d4ed8, #1e40af);
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.btn--outline {
  background-color: transparent;
  color: var(--color-accent-navy);
  border-color: var(--color-border-subtle);
}

.btn--outline:hover {
  background-color: var(--color-primary-soft);
  border-color: var(--color-primary);
}

.btn--ghost {
  background-color: transparent;
  color: var(--color-primary);
}

.btn--ghost:hover {
  background-color: rgba(37, 99, 235, 0.06);
}

.btn:disabled,
.btn[aria-disabled="true"] {
  opacity: 0.6;
  cursor: not-allowed;
  box-shadow: none;
  transform: none;
}

.btn:focus-visible {
  outline: 2px solid var(--color-accent-green);
  outline-offset: 3px;
}

/* Inputs - consistent, calm, cognitive focus */
.input,
textarea,
select {
  width: 100%;
  padding: 0.65rem 0.8rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border-subtle);
  background-color: var(--color-surface);
  color: var(--color-text);
  font-size: var(--font-size-sm);
  transition:
    border-color var(--transition-base),
    box-shadow var(--transition-base),
    background-color var(--transition-base);
}

.input::placeholder,
textarea::placeholder {
  color: var(--color-neutral-400);
}

.input:focus-visible,
textarea:focus-visible,
select:focus-visible {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 1px var(--color-primary-soft);
}

.input[aria-invalid="true"],
textarea[aria-invalid="true"] {
  border-color: var(--color-danger);
}

label {
  display: inline-block;
  margin-bottom: var(--space-1);
  font-size: var(--font-size-sm);
  color: var(--color-text);
}

/* Card - for puzzle previews, feature blocks, etc. */
.card {
  background-color: var(--color-surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border-subtle);
  padding: var(--space-6);
  box-shadow: var(--shadow-xs);
}

.card--elevated {
  box-shadow: var(--shadow-md);
}

.card__header {
  margin-bottom: var(--space-4);
}

.card__title {
  font-size: var(--font-size-lg);
  font-weight: 600;
  color: var(--color-accent-navy);
  margin-bottom: var(--space-1);
}

.card__subtitle {
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}

.card__body {
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}

/* Grid-like visual helpers (for puzzle / logic motifs) */
.logic-grid {
  display: grid;
  grid-auto-rows: minmax(2rem, auto);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border-subtle);
  overflow: hidden;
}

.logic-grid__cell {
  border-right: 1px solid var(--color-border-subtle);
  border-bottom: 1px solid var(--color-border-subtle);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0.35rem;
  font-size: var(--font-size-xs);
}

.logic-grid__cell--header {
  background-color: var(--color-neutral-50);
  font-weight: 500;
}

.logic-grid__cell--highlight {
  background: linear-gradient(135deg, rgba(37, 99, 235, 0.1), rgba(16, 185, 129, 0.12));
}

/* Badges for difficulty levels etc. */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-full);
  font-size: var(--font-size-xs);
  font-weight: 500;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.badge--success {
  background-color: rgba(16, 185, 129, 0.08);
  color: var(--color-accent-green);
}

.badge--info {
  background-color: rgba(37, 99, 235, 0.08);
  color: var(--color-primary);
}

.badge--muted {
  background-color: var(--color-neutral-100);
  color: var(--color-neutral-600);
}

/* ==========================================================
   Media & Imagery
   ========================================================== */
/* Ensure app screens / diagrams sit cleanly in the layout */
.figure {
  margin: 0;
}

.figure__image {
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-md);
}

.figure__caption {
  margin-top: var(--space-2);
  font-size: var(--font-size-xs);
  color: var(--color-neutral-500);
  text-align: center;
}

/* ==========================================================
   Utility Color Accents
   ========================================================== */
.text-muted {
  color: var(--color-text-muted) !important;
}

.text-primary {
  color: var(--color-primary) !important;
}

.text-accent {
  color: var(--color-accent-green) !important;
}

.bg-surface {
  background-color: var(--color-surface) !important;
}

.bg-subtle {
  background-color: var(--color-neutral-50) !important;
}

.border-subtle {
  border: 1px solid var(--color-border-subtle) !important;
}

.border-strong {
  border: 1px solid var(--color-border-strong) !important;
}