/* ==========================================
   Design Tokens & CSS Variables (Editorial Grayscale)
   ========================================== */
:root {
  --font-sans:
    "Geist", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --font-mono: "Geist Mono", "SF Mono", Monaco, monospace;

  /* 4 Primary Shades of Gray on Pure White Background */
  --color-bg: #ffffff; /* Base Background */
  --color-text: #111111; /* Primary Text & Headings */
  --color-text-secondary: #555555; /* Secondary / Reading Text */
  --color-text-muted: #999999; /* Slate / UI Subtext & Comments */
  --color-border: #e8e8e8; /* Soft Grid Borders & Separators */

  --color-editor-bg: #ffffff;
  --color-panel: #ffffff;
  --color-border-active: #111111; /* Accent Color (Pure Black) */

  --color-accent: #111111;
  --color-accent-hover: #333333;
  --color-accent-dim: #f5f5f5;
  --color-accent-highlight: #fafafa;

  /* Minimal Grayscale Code Syntax Tokens */
  --syntax-key: #111111; /* Deep black for keys */
  --syntax-string: #555555; /* Medium charcoal for values */
  --syntax-number: #777777; /* Medium gray for numbers */
  --syntax-boolean: #777777; /* Medium gray for booleans */
  --syntax-comment: #999999; /* Light slate for comments */
  --syntax-punctuation: #b0b0b0; /* Light gray for brackets */

  /* Airy Layout Spacing scale */
  --spacing-xs: 6px;
  --spacing-sm: 12px;
  --spacing-md: 24px;
  --spacing-lg: 40px;
  --spacing-xl: 72px;

  --border-radius: 3px;
  --transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================
   Base Layout & Reset
   ========================================== */
* {
  box-sizing: border-box;
  scrollbar-width: thin;
  scrollbar-color: var(--color-border) transparent;
}

body {
  margin: 0;
  padding: 0;
  background-color: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-sans);
  font-size: 14.5px;
  line-height: 1.65;
  height: 100vh;
  overflow: hidden;
  display: flex;
  justify-content: center;
  -webkit-font-smoothing: antialiased;
}

/* ==========================================
   Airy Center Container
   ========================================== */
#app {
  max-width: 1600px;
  width: 100%;
  height: 100vh;
  padding: 0 var(--spacing-xl);
  display: grid;
  grid-template-areas:
    "header"
    "main";
  grid-template-rows: 84px 1fr;
  grid-template-columns: 100%;
  overflow: hidden;
}

/* ==========================================
   Header Component
   ========================================== */
.header {
  grid-area: header;
  background-color: var(--color-panel);
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0;
  z-index: 10;
}

.brand-section {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.logo {
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: var(--color-text);
  color: #ffffff;
  font-weight: 600;
  font-family: var(--font-mono);
  font-size: 13px;
  width: 26px;
  height: 26px;
  border-radius: 2px;
}

.brand-title {
  font-size: 15px;
  font-weight: 600;
  letter-spacing: -0.02em;
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.brand-tag {
  font-size: 11px;
  font-weight: 500;
  color: var(--color-text-secondary);
  background-color: var(--color-accent-dim);
  padding: 1px 6px;
  border-radius: 2px;
}

.action-bar {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.btn {
  background: none;
  background-color: var(--color-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
  font-family: var(--font-sans);
  font-size: 13px;
  font-weight: 500;
  padding: 7px 14px;
  border-radius: var(--border-radius);
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-sm);
  transition: var(--transition);
}

.btn:hover {
  border-color: var(--color-border-active);
  background-color: var(--color-accent-dim);
}

.btn-primary {
  background-color: var(--color-text);
  color: #ffffff;
  border-color: var(--color-text);
}

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

/* ==========================================
   Main Split-Pane Layout
   ========================================== */
.main-content {
  grid-area: main;
  display: grid;
  grid-template-areas: "editor explainer";
  grid-template-columns: 1.4fr 1fr;
  grid-template-rows: 100%;
  height: 100%;
  width: 100%;
  overflow: hidden;
  column-gap: var(--spacing-xl);
  padding: var(--spacing-md) 0 var(--spacing-xl) 0;
}

/* ==========================================
   Left Editor Pane
   ========================================== */
.editor-pane {
  grid-area: editor;
  background-color: var(--color-editor-bg);
  border-right: 1px solid var(--color-border);
  display: flex;
  flex-direction: column;
  height: 100%;
  overflow: hidden;
  padding-right: var(--spacing-sm);
}

.pane-tabs {
  display: flex;
  background-color: transparent;
  border-bottom: 1px solid var(--color-border);
  height: 40px;
  align-items: flex-end;
  margin-bottom: var(--spacing-md);
}

.pane-tab {
  display: flex;
  align-items: center;
  background: none;
  border: none;
  color: var(--color-text-secondary);
  padding: 8px 0;
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 500;
  margin-right: var(--spacing-md);
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: var(--transition);
}

.pane-tab.active {
  color: var(--color-text);
  border-bottom-color: var(--color-border-active);
  font-weight: 600;
}

.editor-scroll {
  flex: 1;
  overflow: auto;
  font-family: var(--font-mono);
  font-size: 12.5px;
  line-height: 1.6;
  padding-left: 2px;
}

.code-viewport {
  position: relative;
  min-width: max-content;
}

.code-line {
  display: flex;
  align-items: flex-start;
  min-height: 20px;
  padding: 1px 0;
  border-left: 2px solid transparent;
  cursor: pointer;
  transition: background-color 0.1s ease;
}

.code-line:hover {
  background-color: var(--color-accent-highlight);
}

.code-line.active {
  background-color: var(--color-accent-highlight);
  border-left-color: var(--color-border-active);
}

.line-number {
  color: var(--color-text-muted);
  width: 40px;
  text-align: right;
  padding-right: var(--spacing-sm);
  user-select: none;
}

.line-content {
  white-space: pre;
  color: var(--color-text-secondary);
}

/* ==========================================
   Grayscale Syntax Highlighting
   ========================================== */
.token-key {
  color: var(--syntax-key);
  font-weight: 600;
}
.token-string {
  color: var(--syntax-string);
}
.token-number {
  color: var(--syntax-number);
}
.token-boolean {
  color: var(--syntax-boolean);
}
.token-comment {
  color: var(--syntax-comment);
  font-style: italic;
}
.token-punctuation {
  color: var(--syntax-punctuation);
}

/* ==========================================
   Right Explainer Pane
   ========================================== */
.explainer-pane {
  grid-area: explainer;
  background-color: var(--color-bg);
  overflow-y: auto;
  padding: 0 var(--spacing-sm) var(--spacing-xl) 0;
  scroll-behavior: smooth;
}

.explainer-intro {
  margin-bottom: var(--spacing-lg);
  max-width: 580px;
}

.explainer-intro h1 {
  font-size: 28px;
  font-weight: 700;
  margin: 0 0 var(--spacing-sm) 0;
  letter-spacing: -0.03em;
  color: var(--color-text);
}

.explainer-intro p {
  color: var(--color-text-secondary);
  font-size: 14.5px;
  line-height: 1.7;
  margin: 0;
}

.sections-list {
  display: flex;
  flex-direction: column;
  padding-bottom: var(--spacing-xl);
}

/* Minimal card: pure left border, borderless body, high spacing */
.explanation-card {
  background: none;
  border: none;
  border-left: 1.5px solid var(--color-border);
  border-radius: 0;
  padding: 0 0 0 var(--spacing-md);
  margin-bottom: var(--spacing-lg);
  transition: var(--transition);
  scroll-margin-top: var(--spacing-md);
  cursor: pointer;
}

.explanation-card:hover {
  border-left-color: var(--color-text-secondary);
}

.explanation-card.active {
  border-left-color: var(--color-border-active);
}

.card-header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: var(--spacing-sm);
  border: none;
  padding: 0;
}

.card-title {
  font-size: 18px;
  font-weight: 600;
  letter-spacing: -0.02em;
  margin: 0;
  color: var(--color-text);
}

.card-lines {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--color-text-muted);
}

.card-body {
  font-size: 13.5px;
  line-height: 1.7;
  color: var(--color-text-secondary);
}

.card-body p {
  margin: 0 0 var(--spacing-sm) 0;
}

.card-body p:last-child {
  margin-bottom: 0;
}

.card-bullets {
  margin: var(--spacing-sm) 0 var(--spacing-sm) var(--spacing-md);
  padding: 0;
  list-style-type: square;
}

.card-bullets li {
  margin-bottom: var(--spacing-xs);
  color: var(--color-text-secondary);
}

.card-bullets li strong {
  color: var(--color-text);
  font-weight: 600;
}

/* ==========================================
   Minimal Toast Component
   ========================================== */
.toast {
  position: fixed;
  bottom: 32px;
  right: 32px;
  background-color: #ffffff;
  color: var(--color-text);
  padding: 12px 24px;
  border-radius: 2px;
  font-size: 13px;
  font-weight: 500;
  border: 1px solid var(--color-text);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
  transform: translateY(100px);
  opacity: 0;
  transition: all 0.3s cubic-bezier(0.16, 1, 0.3, 1);
  z-index: 1000;
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.toast.show {
  transform: translateY(0);
  opacity: 1;
}

.toast-success-icon {
  color: var(--color-text);
  font-weight: bold;
}

/* ==========================================
   Mobile Responsive Navigation
   ========================================== */
.mobile-tabs {
  display: none;
  grid-template-columns: 1fr 1fr;
  border-bottom: 1px solid var(--color-border);
  background-color: #ffffff;
  margin-bottom: var(--spacing-md);
}

.mobile-tab-btn {
  background: none;
  border: none;
  color: var(--color-text-secondary);
  padding: 14px;
  font-weight: 600;
  font-size: 13px;
  cursor: pointer;
  text-align: center;
  border-bottom: 2px solid transparent;
  transition: var(--transition);
}

.mobile-tab-btn.active {
  color: var(--color-text);
  border-bottom-color: var(--color-border-active);
}

/* ==========================================
   Responsive Adaptations
   ========================================== */
@media (max-width: 900px) {
  #app {
    grid-template-rows: 56px auto 1fr;
    padding: 0 var(--spacing-md);
  }

  .mobile-tabs {
    display: grid;
  }

  .main-content {
    grid-template-areas: "active-pane";
    grid-template-columns: 100%;
    grid-template-rows: 100%;
    column-gap: 0;
    padding: 0;
  }

  .editor-pane {
    display: none;
    grid-area: active-pane;
    border-right: none;
    padding-right: 0;
  }

  .explainer-pane {
    display: none;
    grid-area: active-pane;
    padding: 0 0 var(--spacing-xl) 0;
  }

  .pane-visible {
    display: flex !important;
  }

  .explainer-visible {
    display: block !important;
  }

  .header {
    padding: 0;
  }

  .brand-title {
    font-size: 14px;
  }
}