/* ═══════════════════════════════════════════
   CSS VARIABLES & THEME SYSTEM
   ═══════════════════════════════════════════ */
:root {
  --font-body: 'DM Sans', sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 20px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.1);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.15);
  --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-tertiary: #1c2129;
  --bg-elevated: #21262d;
  --bg-input: #0d1117;
  --border-primary: #30363d;
  --border-secondary: #21262d;
  --border-focus: #58a6ff;
  --text-primary: #e6edf3;
  --text-secondary: #8b949e;
  --text-tertiary: #6e7681;
  --text-link: #58a6ff;
  --accent: #58a6ff;
  --accent-subtle: rgba(88,166,255,0.1);
  --accent-hover: #79c0ff;
  --success: #3fb950;
  --success-subtle: rgba(63,185,80,0.12);
  --error: #f85149;
  --error-subtle: rgba(248,81,73,0.12);
  --warning: #d29922;
  --warning-subtle: rgba(210,153,34,0.12);
  --gradient-accent: linear-gradient(135deg, #58a6ff 0%, #a371f7 100%);
  --shadow-glow: 0 0 20px rgba(88,166,255,0.15);
  --drop-zone-bg: rgba(88,166,255,0.04);
  --drop-zone-active: rgba(88,166,255,0.12);
  --scrollbar-track: #161b22;
  --scrollbar-thumb: #30363d;
  --tag-bg: #1c2129;
}

[data-theme="light"] {
  --bg-primary: #ffffff;
  --bg-secondary: #f6f8fa;
  --bg-tertiary: #eef1f5;
  --bg-elevated: #ffffff;
  --bg-input: #ffffff;
  --border-primary: #d0d7de;
  --border-secondary: #e8ecf0;
  --border-focus: #0969da;
  --text-primary: #1f2328;
  --text-secondary: #656d76;
  --text-tertiary: #8c959f;
  --text-link: #0969da;
  --accent: #0969da;
  --accent-subtle: rgba(9,105,218,0.08);
  --accent-hover: #0550ae;
  --success: #1a7f37;
  --success-subtle: rgba(26,127,55,0.1);
  --error: #cf222e;
  --error-subtle: rgba(207,34,46,0.1);
  --warning: #9a6700;
  --warning-subtle: rgba(154,103,0,0.1);
  --gradient-accent: linear-gradient(135deg, #0969da 0%, #8250df 100%);
  --shadow-glow: 0 0 20px rgba(9,105,218,0.08);
  --drop-zone-bg: rgba(9,105,218,0.03);
  --drop-zone-active: rgba(9,105,218,0.08);
  --scrollbar-track: #f6f8fa;
  --scrollbar-thumb: #d0d7de;
  --tag-bg: #eef1f5;
}

/* ═══════════════════════════════════════════
   RESET & BASE
   ═══════════════════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

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

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  transition: background var(--transition), color var(--transition);
  -webkit-font-smoothing: antialiased;
}

::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--scrollbar-track); }
::-webkit-scrollbar-thumb { background: var(--scrollbar-thumb); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-tertiary); }

::selection {
  background: var(--accent);
  color: #fff;
}

/* ═══════════════════════════════════════════
   SKIP LINK (ACCESSIBILITY)
   ═══════════════════════════════════════════ */
.skip-link {
  position: absolute;
  top: -100%;
  left: 16px;
  z-index: 10000;
  padding: 10px 18px;
  background: var(--accent);
  color: #fff;
  font-family: var(--font-body);
  font-size: 14px;
  font-weight: 600;
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: top 0.2s;
}

.skip-link:focus {
  top: 12px;
}

/* ═══════════════════════════════════════════
   FOCUS INDICATORS (ACCESSIBILITY)
   ═══════════════════════════════════════════ */
:focus-visible {
  outline: 2px solid var(--border-focus);
  outline-offset: 2px;
}

button:focus-visible,
select:focus-visible,
input:focus-visible,
a:focus-visible {
  outline: 2px solid var(--border-focus);
  outline-offset: 2px;
}

.code-area:focus-visible {
  outline: none;
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--accent-subtle);
}

/* ═══════════════════════════════════════════
   LAYOUT
   ═══════════════════════════════════════════ */
.app-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 24px 20px 60px;
}

/* ═══════════════════════════════════════════
   HEADER
   ═══════════════════════════════════════════ */
.site-header {
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-primary);
  padding: 0 24px;
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.header-inner {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text-primary);
}

.logo-icon {
  width: 36px;
  height: 36px;
  background: var(--gradient-accent);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 16px;
  color: #fff;
  flex-shrink: 0;
}

.logo-text {
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 20px;
  letter-spacing: -0.02em;
}

.logo-subtitle {
  display: block;
  font-size: 11px;
  font-weight: 400;
  color: var(--text-secondary);
  letter-spacing: 0.02em;
  line-height: 1;
  margin-top: 2px;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.privacy-badge {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  background: rgba(52, 211, 153, 0.1);
  color: #34d399;
  border-radius: 100px;
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.01em;
}

.privacy-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: #34d399;
  animation: pulse-privacy 2s ease infinite;
}

@keyframes pulse-privacy {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.4; }
}

.theme-toggle {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-primary);
  background: var(--bg-secondary);
  color: var(--text-secondary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
  font-size: 18px;
}

.theme-toggle:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-subtle);
}

/* ═══════════════════════════════════════════
   NAV TABS
   ═══════════════════════════════════════════ */
.nav-tabs {
  display: flex;
  gap: 4px;
  padding: 16px 24px;
  max-width: 1200px;
  margin: 0 auto;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.nav-tab {
  padding: 10px 20px;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  background: transparent;
  color: var(--text-secondary);
  font-family: var(--font-body);
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 8px;
}

.nav-tab .tab-icon {
  font-size: 16px;
}

.nav-tab .tab-label {
  font-size: 14px;
}

.nav-tab:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.nav-tab.active {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

/* ═══════════════════════════════════════════
   CONVERTER PANEL
   ═══════════════════════════════════════════ */
.converter-panel {
  display: none;
  animation: fadeSlideIn 0.3s ease;
}

.converter-panel.active { display: block; }

@keyframes fadeSlideIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ═══════════════════════════════════════════
   SECTION CARD
   ═══════════════════════════════════════════ */
.section-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-primary);
  border-radius: var(--radius-lg);
  padding: 24px;
  margin-bottom: 20px;
  transition: border-color var(--transition);
}

.section-card:focus-within {
  border-color: var(--border-focus);
  box-shadow: var(--shadow-glow);
}

.section-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}

.section-label label {
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-secondary);
}

.section-label .char-count {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--text-tertiary);
}

/* ═══════════════════════════════════════════
   TEXTAREA
   ═══════════════════════════════════════════ */
.code-area {
  width: 100%;
  min-height: 160px;
  padding: 16px;
  border: 1px solid var(--border-secondary);
  border-radius: var(--radius-md);
  background: var(--bg-input);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.65;
  resize: vertical;
  transition: border-color var(--transition), box-shadow var(--transition);
  tab-size: 2;
}

.code-area:focus {
  outline: none;
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--accent-subtle);
}

.code-area::placeholder {
  color: var(--text-tertiary);
  font-style: italic;
}

.code-area.output {
  background: var(--bg-tertiary);
  min-height: 140px;
}

/* ═══════════════════════════════════════════
   ACTION BAR
   ═══════════════════════════════════════════ */
.action-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
  margin-bottom: 20px;
}

.action-group {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 10px 18px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-primary);
  background: var(--bg-elevated);
  color: var(--text-primary);
  font-family: var(--font-body);
  font-size: 13.5px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}

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

.btn:active { transform: scale(0.97); }

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

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

.btn-icon {
  width: 38px;
  height: 38px;
  padding: 0;
  justify-content: center;
  font-size: 16px;
}

.btn-sm {
  padding: 6px 12px;
  font-size: 12px;
}

/* ═══════════════════════════════════════════
   FORMAT SELECTOR
   ═══════════════════════════════════════════ */
.format-row {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 8px;
}

.format-row label {
  font-size: 13px;
  font-weight: 500;
  color: var(--text-secondary);
  min-width: 70px;
}

.format-select {
  padding: 8px 32px 8px 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-primary);
  background: var(--bg-input);
  color: var(--text-primary);
  font-family: var(--font-body);
  font-size: 13px;
  cursor: pointer;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 24 24' fill='none' stroke='%238b949e' stroke-width='2.5' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 10px center;
  transition: border-color var(--transition);
}

.format-select:focus {
  outline: none;
  border-color: var(--border-focus);
}

/* ═══════════════════════════════════════════
   DIRECTION TOGGLE
   ═══════════════════════════════════════════ */
.direction-toggle {
  display: flex;
  align-items: center;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-primary);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.dir-btn {
  padding: 8px 16px;
  border: none;
  background: transparent;
  color: var(--text-secondary);
  font-family: var(--font-body);
  font-size: 12.5px;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
}

.dir-btn.active {
  background: var(--accent);
  color: #fff;
}

/* ═══════════════════════════════════════════
   DROP ZONE
   ═══════════════════════════════════════════ */
.drop-zone {
  border: 2px dashed var(--border-primary);
  border-radius: var(--radius-lg);
  padding: 40px 24px;
  text-align: center;
  background: var(--drop-zone-bg);
  transition: all var(--transition);
  cursor: pointer;
  margin-bottom: 20px;
}

.drop-zone:hover,
.drop-zone.drag-over {
  border-color: var(--accent);
  background: var(--drop-zone-active);
}

.drop-zone.drag-over {
  transform: scale(1.01);
}

.drop-icon {
  font-size: 36px;
  margin-bottom: 12px;
  opacity: 0.6;
}

.drop-zone h2 {
  font-size: 15px;
  font-weight: 600;
  margin-bottom: 6px;
}

.drop-zone p {
  font-size: 13px;
  color: var(--text-secondary);
}

.drop-zone .browse-link {
  color: var(--accent);
  text-decoration: underline;
  cursor: pointer;
}

.file-input-hidden {
  display: none;
}

/* FILE PREVIEW */
.file-preview {
  display: none;
  align-items: center;
  gap: 14px;
  padding: 14px 18px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-primary);
  border-radius: var(--radius-md);
  margin-bottom: 16px;
}

.file-preview.visible { display: flex; }

.file-preview-icon {
  width: 42px;
  height: 42px;
  border-radius: var(--radius-sm);
  background: var(--accent-subtle);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  flex-shrink: 0;
}

.file-preview-info {
  flex: 1;
  min-width: 0;
}

.file-preview-name {
  font-size: 13.5px;
  font-weight: 600;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.file-preview-meta {
  font-size: 12px;
  color: var(--text-secondary);
  margin-top: 2px;
}

.file-preview .btn-remove {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: none;
  background: var(--error-subtle);
  color: var(--error);
  font-size: 16px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
  flex-shrink: 0;
}

.file-preview .btn-remove:hover {
  background: var(--error);
  color: #fff;
}

/* ═══════════════════════════════════════════
   STATUS / TOAST
   ═══════════════════════════════════════════ */
.status-bar {
  display: none;
  align-items: center;
  gap: 8px;
  padding: 10px 16px;
  border-radius: var(--radius-md);
  font-size: 13px;
  font-weight: 500;
  margin-bottom: 16px;
  animation: fadeSlideIn 0.25s ease;
}

.status-bar.visible { display: flex; }

.status-bar.success {
  background: var(--success-subtle);
  color: var(--success);
  border: 1px solid var(--success);
}

.status-bar.error {
  background: var(--error-subtle);
  color: var(--error);
  border: 1px solid var(--error);
}

.status-bar.info {
  background: var(--accent-subtle);
  color: var(--accent);
  border: 1px solid var(--accent);
}

.status-bar.warning {
  background: var(--warning-subtle);
  color: var(--warning);
  border: 1px solid var(--warning);
}

/* ═══════════════════════════════════════════
   ENCODING TAGS (for quick info)
   ═══════════════════════════════════════════ */
.encoding-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 12px;
}

.tag {
  padding: 4px 10px;
  border-radius: 999px;
  background: var(--tag-bg);
  border: 1px solid var(--border-secondary);
  font-size: 11.5px;
  font-family: var(--font-mono);
  color: var(--text-secondary);
  font-weight: 500;
}

/* ═══════════════════════════════════════════
   SWAP BUTTON
   ═══════════════════════════════════════════ */
.swap-row {
  display: flex;
  justify-content: center;
  margin: -6px 0;
  position: relative;
  z-index: 2;
}

.btn-swap {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 2px solid var(--border-primary);
  background: var(--bg-secondary);
  color: var(--text-secondary);
  font-size: 18px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
}

.btn-swap:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-subtle);
  transform: rotate(180deg);
}

/* ═══════════════════════════════════════════
   FOOTER
   ═══════════════════════════════════════════ */
.app-footer {
  text-align: center;
  padding: 32px 0 0;
  border-top: 1px solid var(--border-primary);
  margin-top: 40px;
}

.app-footer p {
  font-size: 12.5px;
  color: var(--text-tertiary);
}

.app-footer .privacy-note {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--success-subtle);
  color: var(--success);
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 600;
  margin-bottom: 12px;
}

/* ═══════════════════════════════════════════
   RESPONSIVE
   ═══════════════════════════════════════════ */
@media (max-width: 640px) {
  .app-container { padding: 16px 14px 40px; }
  .header-inner { height: 56px; }
  .logo-text { font-size: 17px; }
  .nav-tabs { gap: 4px; padding: 12px 16px; }
  .nav-tab { padding: 8px 14px; font-size: 13px; }
  .nav-tab .tab-label { font-size: 13px; }
  .section-card { padding: 16px; }
  .code-area { min-height: 120px; font-size: 12.5px; padding: 12px; }
  .action-bar { gap: 8px; }
  .btn { padding: 8px 14px; font-size: 12.5px; }
  .drop-zone { padding: 28px 16px; }
  .format-row { gap: 8px; }
}

/* ═══════════════════════════════════════════
   IMAGE PREVIEW IN FILE PANEL
   ═══════════════════════════════════════════ */
.image-thumb {
  max-width: 100%;
  max-height: 200px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-primary);
  margin-top: 12px;
  display: none;
}

.image-thumb.visible { display: block; }

/* Utility */
.gap-sm { gap: 8px; }
.mb-12 { margin-bottom: 12px; }
.mt-8 { margin-top: 8px; }
.flex-wrap { flex-wrap: wrap; }

/* ===== SITE FOOTER ===== */
.site-footer{
  margin-top:60px;padding:48px 28px 36px;
  border-top:1px solid var(--border-primary);
  background:var(--bg-primary);color:var(--text-secondary);
  font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;
  font-size:14px;line-height:1.6;
}
.site-footer .footer-inner{max-width:1100px;margin:0 auto}
.site-footer .footer-grid{
  display:grid;grid-template-columns:2fr 1fr 1fr 1fr;
  gap:40px;margin-bottom:40px;
}
.site-footer .footer-brand{display:flex;align-items:center;gap:10px;margin-bottom:16px}
.site-footer .footer-brand svg{width:32px;height:32px;color:#a855f7;flex-shrink:0}
.site-footer .footer-brand-name{
  font-size:20px;font-weight:700;
  background:linear-gradient(90deg,#8B5CF6,#EC4899,#3B82F6);
  -webkit-background-clip:text;-webkit-text-fill-color:transparent;background-clip:text;
}
.site-footer .footer-desc{color:var(--text-tertiary);margin-bottom:16px;max-width:360px}
.site-footer .footer-copy{font-size:12px;color:var(--text-tertiary);opacity:.7}
.site-footer h4{font-weight:700;margin-bottom:16px;color:var(--text-primary);font-size:15px}
.site-footer ul{list-style:none;padding:0;margin:0;display:flex;flex-direction:column;gap:10px}
.site-footer a{color:var(--text-secondary);text-decoration:none;transition:color .2s}
.site-footer a:hover{color:#a855f7}
.site-footer .footer-bottom{
  border-top:1px solid var(--border-primary);
  padding-top:20px;text-align:center;
}
.site-footer .footer-bottom p{color:var(--text-tertiary);font-size:13px;opacity:.7}
.site-footer .footer-bottom span{color:#a855f7}

@media(max-width:768px){
  .site-footer .footer-grid{grid-template-columns:1fr;gap:32px}
  .site-footer{padding:36px 16px 28px}
}
.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}