/* ============================================
   ToolChemy.com — Design System
   Mobile-first, system font stack, single file
   ============================================ */

/* --- CSS Custom Properties --- */
:root {
  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
               "Helvetica Neue", Arial, "Noto Sans", sans-serif,
               "Apple Color Emoji", "Segoe UI Emoji";
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;

  /* Type Scale (1.25 ratio) */
  --text-xs:   0.75rem;
  --text-sm:   0.875rem;
  --text-base: 1rem;
  --text-lg:   1.125rem;
  --text-xl:   1.25rem;
  --text-2xl:  1.563rem;
  --text-3xl:  1.953rem;
  --text-4xl:  2.441rem;

  /* Spacing (4px base) */
  --space-1:  0.25rem;
  --space-2:  0.5rem;
  --space-3:  0.75rem;
  --space-4:  1rem;
  --space-6:  1.5rem;
  --space-8:  2rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;

  /* Colors */
  --color-primary:      #2563eb;
  --color-primary-dark:  #1d4ed8;
  --color-primary-light: #dbeafe;
  --color-accent:       #7c3aed;
  --color-text:         #1f2937;
  --color-text-muted:   #6b7280;
  --color-bg:           #ffffff;
  --color-bg-alt:       #f9fafb;
  --color-border:       #e5e7eb;
  --color-success:      #059669;
  --color-warning:      #d97706;
  --color-error:        #dc2626;

  /* Layout */
  --max-width:     1200px;
  --content-width: 800px;
  --radius-sm:  0.375rem;
  --radius-md:  0.5rem;
  --radius-lg:  0.75rem;
  --shadow-sm:  0 1px 2px rgba(0,0,0,0.05);
  --shadow-md:  0 4px 6px -1px rgba(0,0,0,0.1), 0 2px 4px -2px rgba(0,0,0,0.1);
  --shadow-lg:  0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -4px rgba(0,0,0,0.1);
}

/* --- Reset --- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

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

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

/* --- Base Typography --- */
body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
}

h1, h2, h3, h4, h5, h6 {
  line-height: 1.25;
  font-weight: 700;
  color: var(--color-text);
}

h1 { font-size: var(--text-3xl); margin-bottom: var(--space-6); }
h2 { font-size: var(--text-2xl); margin-bottom: var(--space-4); }
h3 { font-size: var(--text-xl);  margin-bottom: var(--space-3); }
h4 { font-size: var(--text-lg);  margin-bottom: var(--space-2); }

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

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color 0.2s ease;
}

a:hover {
  color: var(--color-primary-dark);
  text-decoration: underline;
}

ul, ol {
  padding-left: var(--space-6);
  margin-bottom: var(--space-4);
}

li {
  margin-bottom: var(--space-2);
}

code {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  background: var(--color-bg-alt);
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-sm);
}

/* --- Layout --- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-4);
}

/* --- Header --- */
.site-header {
  background: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.site-logo {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-xl);
  font-weight: 800;
  color: var(--color-primary);
  text-decoration: none;
  letter-spacing: -0.02em;
}

.site-logo:hover {
  color: var(--color-primary-dark);
  text-decoration: none;
}

.site-logo span {
  color: var(--color-accent);
}

.logo-img {
  height: 36px;
  width: 36px;
  border-radius: var(--radius-sm);
  flex-shrink: 0;
}

.footer-logo {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  text-decoration: none;
  color: var(--color-bg);
  font-weight: 700;
  font-size: var(--text-base);
  margin-bottom: var(--space-4);
}

.footer-logo:hover {
  color: var(--color-bg);
  text-decoration: none;
}

.footer-logo img {
  height: 28px;
  width: 28px;
  border-radius: var(--radius-sm);
  flex-shrink: 0;
}

.nav-toggle {
  display: flex;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-2);
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  transition: transform 0.2s ease;
}

.main-nav {
  display: none;
  position: absolute;
  top: 64px;
  left: 0;
  right: 0;
  background: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-md);
}

.main-nav.is-open {
  display: block;
}

.main-nav ul {
  list-style: none;
  padding: var(--space-4);
  margin: 0;
}

.main-nav li {
  margin: 0;
}

.main-nav a {
  display: block;
  padding: var(--space-3) var(--space-4);
  color: var(--color-text);
  font-weight: 500;
  border-radius: var(--radius-sm);
}

.main-nav a:hover {
  background: var(--color-bg-alt);
  text-decoration: none;
  color: var(--color-primary);
}

/* --- Breadcrumb --- */
.breadcrumb {
  background: var(--color-bg-alt);
  padding: var(--space-3) 0;
  font-size: var(--text-sm);
}

.breadcrumb ol {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  padding: 0;
  margin: 0;
}

.breadcrumb li::after {
  content: "/";
  margin-left: var(--space-2);
  color: var(--color-text-muted);
}

.breadcrumb li:last-child::after {
  content: "";
}

.breadcrumb a {
  color: var(--color-text-muted);
}

.breadcrumb a:hover {
  color: var(--color-primary);
}

.breadcrumb [aria-current="page"] {
  color: var(--color-text);
  font-weight: 500;
}

/* --- Hero Section (Homepage) --- */
.hero {
  background: linear-gradient(135deg, var(--color-primary-light) 0%, var(--color-bg) 100%);
  padding: var(--space-16) 0;
  text-align: center;
}

.hero h1 {
  font-size: var(--text-3xl);
  max-width: var(--content-width);
  margin: 0 auto var(--space-4);
}

.hero-subtitle {
  font-size: var(--text-lg);
  color: var(--color-text-muted);
  max-width: 600px;
  margin: 0 auto;
}

/* --- Category Cards Grid --- */
.tool-categories-section,
.featured-tools,
.about-section {
  padding: var(--space-12) 0;
}

.tool-categories-section h2,
.featured-tools h2 {
  text-align: center;
  margin-bottom: var(--space-8);
}

.tool-categories {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-6);
}

.category-card {
  display: block;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  box-shadow: var(--shadow-sm);
  transition: box-shadow 0.2s ease, transform 0.2s ease;
  text-decoration: none;
  color: var(--color-text);
}

.category-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
  text-decoration: none;
  color: var(--color-text);
}

.card-icon {
  font-size: var(--text-4xl);
  margin-bottom: var(--space-3);
}

.category-card h3 {
  color: var(--color-text);
  margin-bottom: var(--space-2);
}

.category-card p {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  margin-bottom: var(--space-3);
}

.card-cta {
  color: var(--color-primary);
  font-weight: 600;
  font-size: var(--text-sm);
}

/* --- Featured Tools Grid --- */
.featured-tools {
  background: var(--color-bg-alt);
}

.featured-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-4);
}

.featured-card {
  display: block;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-6);
  text-decoration: none;
  color: var(--color-text);
  transition: box-shadow 0.2s ease;
}

.featured-card:hover {
  box-shadow: var(--shadow-md);
  text-decoration: none;
  color: var(--color-text);
}

.featured-card h3 {
  font-size: var(--text-lg);
  color: var(--color-primary);
  margin-bottom: var(--space-2);
}

.featured-card p {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  margin: 0;
}

/* --- About Section --- */
.about-section {
  max-width: var(--content-width);
  margin: 0 auto;
  padding-left: var(--space-4);
  padding-right: var(--space-4);
}

/* --- Tool Widget Area --- */
.tool-widget-area {
  max-width: var(--max-width);
  margin: var(--space-8) auto;
  padding: var(--space-6);
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
}

/* --- Article Content --- */
.article-content {
  max-width: var(--content-width);
  margin: 0 auto;
  padding: var(--space-8) var(--space-4);
  line-height: 1.75;
  font-size: var(--text-lg);
}

.article-content h2 {
  font-size: var(--text-2xl);
  margin-top: var(--space-12);
  margin-bottom: var(--space-4);
  padding-top: var(--space-4);
  border-top: 1px solid var(--color-border);
}

.article-content h2:first-of-type {
  border-top: none;
  padding-top: 0;
}

.article-content h3 {
  margin-top: var(--space-8);
}

.article-content p {
  margin-bottom: var(--space-4);
}

.article-content ul,
.article-content ol {
  margin-bottom: var(--space-6);
}

.article-content figure {
  margin: var(--space-8) 0;
}

.article-content figcaption {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  text-align: center;
  margin-top: var(--space-2);
}

.article-content img {
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
}

.article-content table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: var(--space-6);
  font-size: var(--text-base);
}

.article-content th,
.article-content td {
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--color-border);
  text-align: left;
}

.article-content th {
  background: var(--color-bg-alt);
  font-weight: 600;
}

.article-content tr:nth-child(even) {
  background: var(--color-bg-alt);
}

/* --- Key Takeaways Box --- */
.key-takeaways {
  background: var(--color-primary-light);
  border-left: 4px solid var(--color-primary);
  border-radius: var(--radius-md);
  padding: var(--space-6);
  margin-bottom: var(--space-8);
  max-width: var(--content-width);
  margin-left: auto;
  margin-right: auto;
}

.key-takeaways h2 {
  font-size: var(--text-lg);
  margin-bottom: var(--space-3);
  border: none;
  padding: 0;
  margin-top: 0;
}

.key-takeaways ul {
  margin: 0;
}

.key-takeaways li {
  margin-bottom: var(--space-2);
}

.key-takeaways li:last-child {
  margin-bottom: 0;
}

/* --- FAQ Accordion --- */
.faq-section {
  max-width: var(--content-width);
  margin: 0 auto;
  padding: var(--space-8) var(--space-4) var(--space-12);
}

.faq-section > h2 {
  margin-bottom: var(--space-6);
}

.faq-item {
  border-bottom: 1px solid var(--color-border);
}

.faq-item summary {
  cursor: pointer;
  font-weight: 600;
  padding: var(--space-4) 0;
  list-style: none;
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-size: var(--text-lg);
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::before {
  content: "+";
  font-size: var(--text-xl);
  font-weight: 700;
  color: var(--color-primary);
  flex-shrink: 0;
  width: 1.5em;
  text-align: center;
}

.faq-item[open] summary::before {
  content: "\2212";
}

.faq-answer {
  padding: 0 0 var(--space-4) 2.25em;
  color: var(--color-text-muted);
  line-height: 1.7;
}

.faq-answer p:last-child {
  margin-bottom: 0;
}

/* --- Related Tools --- */
.related-tools {
  max-width: var(--content-width);
  margin: 0 auto;
  padding: 0 var(--space-4) var(--space-12);
}

.related-tools h2 {
  margin-bottom: var(--space-6);
}

.related-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-4);
}

.related-card {
  display: block;
  padding: var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: box-shadow 0.2s ease;
}

.related-card:hover {
  box-shadow: var(--shadow-md);
  text-decoration: none;
}

.related-card h3 {
  color: var(--color-primary);
  font-size: var(--text-base);
  margin-bottom: var(--space-1);
}

.related-card p {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  margin: 0;
}

/* --- Footer --- */
.site-footer {
  background: var(--color-text);
  color: #d1d5db;
  padding: var(--space-12) 0 var(--space-6);
}

.footer-inner {
  display: flex;
  flex-direction: column;
  gap: var(--space-8);
}

.footer-links {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-6);
}

.footer-col h4 {
  color: var(--color-bg);
  font-size: var(--text-sm);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-3);
}

.footer-col ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.footer-col li {
  margin-bottom: var(--space-2);
}

.footer-col a {
  color: #9ca3af;
  font-size: var(--text-sm);
  transition: color 0.2s ease;
}

.footer-col a:hover {
  color: var(--color-bg);
  text-decoration: none;
}

.footer-bottom {
  border-top: 1px solid #374151;
  padding-top: var(--space-6);
  text-align: center;
  font-size: var(--text-sm);
  color: #9ca3af;
}

/* --- Calculator Widget --- */
.calc-display {
  background: var(--color-text);
  color: var(--color-bg);
  border-radius: var(--radius-md);
  padding: var(--space-4) var(--space-6);
  margin-bottom: var(--space-4);
  text-align: right;
  min-height: 80px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}

.calc-expression {
  font-size: var(--text-sm);
  color: #9ca3af;
  min-height: 1.5em;
  word-break: break-all;
}

.calc-result {
  font-size: var(--text-3xl);
  font-family: var(--font-mono);
  font-weight: 700;
  word-break: break-all;
}

.calc-mode-toggle {
  display: flex;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
}

.calc-mode-btn {
  padding: var(--space-2) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  cursor: pointer;
  font-size: var(--text-sm);
  font-weight: 600;
  transition: all 0.2s ease;
}

.calc-mode-btn.active {
  background: var(--color-primary);
  color: var(--color-bg);
  border-color: var(--color-primary);
}

.calc-buttons {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: var(--space-2);
}

.calc-btn {
  padding: var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg);
  cursor: pointer;
  font-size: var(--text-base);
  font-weight: 500;
  min-height: 48px;
  transition: all 0.15s ease;
  font-family: var(--font-sans);
}

.calc-btn:hover {
  background: var(--color-bg-alt);
}

.calc-btn:active {
  transform: scale(0.95);
}

.calc-btn.operator {
  background: var(--color-primary-light);
  color: var(--color-primary);
  font-weight: 700;
}

.calc-btn.operator:hover {
  background: var(--color-primary);
  color: var(--color-bg);
}

.calc-btn.func {
  background: var(--color-bg-alt);
  font-size: var(--text-sm);
}

.calc-btn.func:hover {
  background: var(--color-border);
}

.calc-btn.equals {
  background: var(--color-success);
  color: var(--color-bg);
  font-weight: 700;
}

.calc-btn.equals:hover {
  background: #047857;
}

.calc-btn.clear {
  background: var(--color-error);
  color: var(--color-bg);
  font-weight: 700;
}

.calc-btn.clear:hover {
  background: #b91c1c;
}

/* --- Color Picker Widgets --- */
.upload-zone {
  border: 2px dashed var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-12) var(--space-8);
  text-align: center;
  cursor: pointer;
  transition: border-color 0.2s ease, background 0.2s ease;
}

.upload-zone:hover,
.upload-zone.drag-over {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

.upload-zone input[type="file"] {
  display: none;
}

.upload-zone p {
  color: var(--color-text-muted);
  margin: 0;
}

.image-canvas-wrapper {
  position: relative;
  margin: var(--space-4) 0;
  cursor: crosshair;
}

.image-canvas-wrapper canvas {
  max-width: 100%;
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
}

.color-output {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-4);
  padding: var(--space-4);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  margin-top: var(--space-4);
}

.color-swatch {
  width: 64px;
  height: 64px;
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  flex-shrink: 0;
}

.color-values {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  flex: 1;
}

.color-values label {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-text-muted);
}

.color-values input {
  flex: 1;
  padding: var(--space-2) var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  background: var(--color-bg-alt);
}

.picked-colors {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-4);
}

.picked-color {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  border: 2px solid var(--color-border);
  cursor: pointer;
  transition: transform 0.15s ease;
}

.picked-color:hover {
  transform: scale(1.15);
}

/* --- Color Picker (HTML / Hex) --- */
.picker-main {
  display: flex;
  align-items: center;
  gap: var(--space-6);
  margin-bottom: var(--space-6);
}

.picker-main input[type="color"] {
  width: 80px;
  height: 80px;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  padding: 0;
}

.color-preview {
  flex: 1;
  height: 80px;
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
  transition: background-color 0.2s ease;
}

.color-inputs {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-4);
  margin-bottom: var(--space-6);
}

.input-group {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.input-group label {
  font-weight: 700;
  font-size: var(--text-sm);
  min-width: 3em;
  color: var(--color-text-muted);
}

.input-group input {
  flex: 1;
  padding: var(--space-2) var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-base);
}

.input-group input[type="number"] {
  max-width: 80px;
}

.color-harmonies {
  margin-bottom: var(--space-6);
}

.color-harmonies h3 {
  font-size: var(--text-base);
  margin-bottom: var(--space-3);
}

.harmony-row {
  display: flex;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
  align-items: center;
}

.harmony-label {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-text-muted);
  min-width: 120px;
}

.harmony-swatch {
  width: 48px;
  height: 32px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--color-border);
  cursor: pointer;
}

.css-output {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-3) var(--space-4);
  background: var(--color-text);
  border-radius: var(--radius-md);
  margin-top: var(--space-4);
}

.css-output code {
  flex: 1;
  color: #e5e7eb;
  background: transparent;
  font-size: var(--text-sm);
}

/* --- Hex Color Picker Specific --- */
.hex-main-input {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  margin-bottom: var(--space-6);
}

.hex-main-input input[type="text"] {
  font-size: var(--text-2xl);
  font-family: var(--font-mono);
  font-weight: 700;
  padding: var(--space-3) var(--space-4);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  max-width: 200px;
  text-align: center;
}

.hex-main-input input[type="text"]:focus {
  outline: none;
  border-color: var(--color-primary);
}

.color-ref-table {
  width: 100%;
  border-collapse: collapse;
}

.color-ref-table td {
  padding: var(--space-2) var(--space-3);
  border: 1px solid var(--color-border);
  font-size: var(--text-sm);
}

.color-ref-swatch {
  width: 32px;
  height: 24px;
  border-radius: var(--radius-sm);
  display: inline-block;
  vertical-align: middle;
  border: 1px solid var(--color-border);
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border: none;
  border-radius: var(--radius-md);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
}

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

.btn-primary:hover {
  background: var(--color-primary-dark);
}

.btn-secondary {
  background: var(--color-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
}

.btn-secondary:hover {
  background: var(--color-bg-alt);
}

.btn-copy {
  background: var(--color-bg);
  color: var(--color-text-muted);
  border: 1px solid var(--color-border);
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
}

.btn-copy:hover {
  background: var(--color-primary);
  color: var(--color-bg);
  border-color: var(--color-primary);
}

.btn-copy.copied {
  background: var(--color-success);
  color: var(--color-bg);
  border-color: var(--color-success);
}

/* --- Comparison Table --- */
.comparison-table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-6) 0;
  font-size: var(--text-sm);
}

.comparison-table th {
  background: var(--color-primary);
  color: var(--color-bg);
  padding: var(--space-3) var(--space-4);
  text-align: left;
}

.comparison-table td {
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--color-border);
}

.comparison-table tr:nth-child(even) {
  background: var(--color-bg-alt);
}

/* --- Responsive: Tablet (640px+) --- */
@media (min-width: 640px) {
  .hero h1 {
    font-size: var(--text-4xl);
  }

  .tool-categories {
    grid-template-columns: repeat(2, 1fr);
  }

  .featured-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .footer-links {
    grid-template-columns: repeat(2, 1fr);
  }

  .related-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .color-inputs {
    grid-template-columns: repeat(3, 1fr);
  }
}

/* --- Responsive: Desktop (1024px+) --- */
@media (min-width: 1024px) {
  h1 { font-size: var(--text-4xl); }

  .nav-toggle {
    display: none;
  }

  .main-nav {
    display: block;
    position: static;
    background: transparent;
    border: none;
    box-shadow: none;
  }

  .main-nav ul {
    display: flex;
    gap: var(--space-1);
    padding: 0;
  }

  .main-nav a {
    padding: var(--space-2) var(--space-3);
  }

  .tool-categories {
    grid-template-columns: repeat(3, 1fr);
  }

  .featured-grid {
    grid-template-columns: repeat(3, 1fr);
  }

  .footer-links {
    grid-template-columns: repeat(5, 1fr);
  }

  .related-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

/* --- Calculator: Result Row with Copy Button --- */
.calc-result-row {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: var(--space-2);
}

.calc-result-row .calc-result {
  flex: 1;
  min-width: 0;
}

.calc-copy-btn {
  flex-shrink: 0;
  background: transparent;
  border: 1px solid rgba(255,255,255,0.2);
  color: #9ca3af;
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-sm);
  font-size: var(--text-xs);
  font-family: var(--font-sans);
  cursor: pointer;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.calc-copy-btn:hover {
  background: rgba(255,255,255,0.1);
  color: var(--color-bg);
  border-color: rgba(255,255,255,0.4);
}

.calc-copy-btn.copied {
  background: var(--color-success);
  color: var(--color-bg);
  border-color: var(--color-success);
}

/* --- Calculator: Tab Navigation --- */
.calc-tabs {
  display: flex;
  border-bottom: 2px solid var(--color-border);
  margin-bottom: var(--space-4);
  gap: 0;
}

.calc-tab {
  flex: 1;
  padding: var(--space-3) var(--space-4);
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  margin-bottom: -2px;
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-text-muted);
  cursor: pointer;
  transition: all 0.2s ease;
  text-align: center;
}

.calc-tab:hover {
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.calc-tab[aria-selected="true"] {
  color: var(--color-primary);
  border-bottom-color: var(--color-primary);
}

.calc-tab-panel {
  display: none;
  animation: fadeIn 0.2s ease;
}

.calc-tab-panel.active {
  display: block;
}

/* --- Calculator: Extended Buttons (More) --- */
.calc-more-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  width: 100%;
  padding: var(--space-2);
  margin-top: var(--space-2);
  background: none;
  border: 1px dashed var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
}

.calc-more-toggle:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.calc-more-toggle .arrow {
  display: inline-block;
  transition: transform 0.2s ease;
}

.calc-more-toggle.open .arrow {
  transform: rotate(180deg);
}

.calc-buttons-extended {
  display: none;
  grid-template-columns: repeat(5, 1fr);
  gap: var(--space-2);
  margin-top: var(--space-2);
  padding-top: var(--space-3);
  border-top: 1px dashed var(--color-border);
}

.calc-buttons-extended.open {
  display: grid;
}

/* --- Calculator: Error State --- */
.calc-result.is-error {
  color: #f87171;
  font-size: var(--text-lg);
}

/* --- Calculator: History Panel --- */
.calc-history {
  max-height: 400px;
  overflow-y: auto;
  padding: var(--space-2) 0;
}

.calc-history-item {
  display: flex;
  flex-direction: column;
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--color-border);
  cursor: pointer;
  transition: background 0.15s ease;
  border-radius: var(--radius-sm);
}

.calc-history-item:hover {
  background: var(--color-primary-light);
}

.calc-history-expr {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  word-break: break-all;
}

.calc-history-result {
  font-size: var(--text-lg);
  font-weight: 700;
  font-family: var(--font-mono);
  color: var(--color-text);
}

.calc-history-empty {
  text-align: center;
  padding: var(--space-8);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.calc-history-clear {
  display: block;
  width: 100%;
  padding: var(--space-2);
  margin-top: var(--space-2);
  background: none;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  cursor: pointer;
  transition: all 0.2s ease;
}

.calc-history-clear:hover {
  background: var(--color-error);
  color: var(--color-bg);
  border-color: var(--color-error);
}

/* --- Calculator: Quick-Graph Panel --- */
.calc-quickgraph {
  text-align: center;
}

.calc-quickgraph canvas {
  width: 100%;
  max-width: 600px;
  height: 300px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg);
}

.calc-quickgraph-hint {
  padding: var(--space-8);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  text-align: center;
}

.calc-quickgraph-info {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  margin-top: var(--space-3);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.calc-quickgraph-info a {
  font-weight: 600;
}

/* --- Graphing Calculator: Canvas Wrapper --- */
.graph-canvas-wrapper {
  position: relative;
  margin: var(--space-4) 0;
}

/* --- Graphing Calculator: Coordinate Tooltip --- */
.graph-coords {
  position: absolute;
  top: var(--space-2);
  right: var(--space-2);
  background: rgba(31, 41, 55, 0.85);
  color: var(--color-bg);
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.15s ease;
  z-index: 10;
  white-space: nowrap;
}

.graph-coords.visible {
  opacity: 1;
}

/* --- Graphing Calculator: Controls Bar --- */
.graph-controls {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
}

.graph-controls .btn {
  min-height: 36px;
}

/* --- Graphing Calculator: Snap to Grid --- */
.graph-snap-label {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  cursor: pointer;
  padding: var(--space-1) var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  transition: all 0.2s ease;
  user-select: none;
}

.graph-snap-label:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.graph-snap-label input[type="checkbox"] {
  accent-color: var(--color-primary);
}

/* --- Graphing Calculator: Function Table --- */
.graph-table-panel {
  display: none;
  margin-top: var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.graph-table-panel.open {
  display: block;
}

.graph-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--text-sm);
  font-family: var(--font-mono);
}

.graph-table thead {
  background: var(--color-bg-alt);
  position: sticky;
  top: 0;
}

.graph-table th,
.graph-table td {
  padding: var(--space-2) var(--space-3);
  text-align: right;
  border-bottom: 1px solid var(--color-border);
  white-space: nowrap;
}

.graph-table th {
  font-weight: 700;
  color: var(--color-text);
  border-right: 1px solid var(--color-border);
}

.graph-table th:last-child {
  border-right: none;
}

.graph-table td {
  border-right: 1px solid var(--color-border);
}

.graph-table td:last-child {
  border-right: none;
}

.graph-table tbody tr:hover {
  background: var(--color-primary-light);
}

.graph-table-scroll {
  max-height: 300px;
  overflow-y: auto;
}

/* --- Graphing Calculator: Equation Input Row --- */
.graph-equation-input {
  display: flex;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
}

.graph-equation-input input {
  flex: 1;
  padding: var(--space-3) var(--space-4);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
  font-size: var(--text-base);
  transition: border-color 0.2s ease;
}

.graph-equation-input input:focus {
  outline: none;
  border-color: var(--color-primary);
}

/* --- Ad Containers --- */
.ad-container {
  display: flex;
  justify-content: center;
  align-items: center;
  margin: var(--space-8) auto;
  max-width: var(--content-width);
  padding: 0 var(--space-4);
  overflow: hidden;
  clear: both;
}

.ad-container-widget {
  max-width: var(--max-width);
  padding: 0;
}

.ad-container-sticky {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  z-index: 900;
  display: none;
  justify-content: center;
  align-items: center;
  background: rgba(255, 255, 255, 0.98);
  padding: var(--space-2) 0;
  box-shadow: 0 -2px 10px rgba(0, 0, 0, 0.08);
}

.ad-container-sticky .ad-close {
  position: absolute;
  top: -10px;
  right: 8px;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  border: 1px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text-muted);
  font-size: 14px;
  line-height: 1;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
  z-index: 1;
}

.ad-container-sticky .ad-close:hover {
  background: var(--color-error);
  color: var(--color-bg);
  border-color: var(--color-error);
}

@media (max-width: 639px) {
  .ad-container-sticky {
    display: flex;
  }

  .site-footer {
    padding-bottom: 116px;
  }
}

/* --- Animation --- */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(4px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* --- Responsive: Small screens --- */
@media (max-width: 639px) {
  .calc-tab {
    padding: var(--space-2) var(--space-3);
    font-size: var(--text-xs);
  }

  .calc-buttons-extended {
    grid-template-columns: repeat(3, 1fr);
  }

  .graph-controls {
    flex-direction: column;
  }

  .graph-controls .btn {
    width: 100%;
    justify-content: center;
  }

  .graph-equation-input {
    flex-direction: column;
  }

  .graph-table {
    font-size: var(--text-xs);
  }
}

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

.text-center { text-align: center; }
.text-muted { color: var(--color-text-muted); }
.mt-4 { margin-top: var(--space-4); }
.mb-4 { margin-bottom: var(--space-4); }
.mt-8 { margin-top: var(--space-8); }
.mb-8 { margin-bottom: var(--space-8); }