:root {
  /* Colors */
  --primary-color: #4f46e5;
  --primary-hover: #4338ca;
  --bg-color: #ffffff;
  --text-color: #0f172a;
  --text-muted: #64748b;
  --border-color: #e2e8f0;
  --header-bg: #ffffff;
  --footer-bg: #f8fafc;
  --card-bg: #ffffff;
  --panel-bg: #f8fafc;
  
  --success-color: #10b981;
  --warning-color: #f59e0b;
  --error-color: #ef4444;

  /* Typography */
  --font-family: 'Inter', system-ui, -apple-system, sans-serif;
  
  /* Spacing Scale */
  --space-1: 0.25rem;  /* 4px */
  --space-2: 0.5rem;   /* 8px */
  --space-3: 0.75rem;  /* 12px */
  --space-4: 1rem;     /* 16px */
  --space-5: 1.5rem;   /* 24px */
  --space-6: 2rem;     /* 32px */
  --space-8: 3rem;     /* 48px */
  --space-10: 4rem;    /* 64px */

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
  --focus-ring: 0 0 0 3px rgba(79, 70, 229, 0.2);
}

[data-theme="dark"] {
  --primary-color: #818cf8;
  --primary-hover: #a5b4fc;
  --bg-color: #0f172a;
  --text-color: #f8fafc;
  --text-muted: #94a3b8;
  --border-color: #334155;
  --header-bg: #0f172a;
  --footer-bg: #020617;
  --card-bg: #1e293b;
  --panel-bg: #0f172a;
  
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.5);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.5);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.5);
  --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.5);
  --focus-ring: 0 0 0 3px rgba(129, 140, 248, 0.2);
}

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-color);
  color: var(--text-color);
  line-height: 1.6;
  font-size: 16px;
  overflow-x: hidden;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

main { flex: 1; }

a { color: var(--primary-color); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--primary-hover); }
ul { list-style: none; }

/* Container */
.container {
  width: 100%;
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 var(--space-4);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  line-height: 1.2;
  margin-bottom: var(--space-4);
  color: var(--text-color);
  letter-spacing: -0.02em;
}
h1 { font-size: 2.5rem; font-weight: 800; }
h2 { font-size: 2rem; font-weight: 700; }
h3 { font-size: 1.5rem; font-weight: 600; }
p { margin-bottom: var(--space-4); }

/* Layout Utilities */
.grid { display: grid; gap: var(--space-6); }
.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-between { justify-content: space-between; }
.flex-responsive { display: flex; flex-direction: column; gap: var(--space-4); }
@media (min-width: 640px) { .flex-responsive { flex-direction: row; align-items: center; } }

/* Sticky Header */
.site-header {
  background-color: var(--header-bg);
  padding: var(--space-3) 0;
  position: sticky;
  top: 0;
  z-index: 100;
  transition: all 0.3s ease;
  border-bottom: 1px solid transparent;
}
.site-header.scrolled {
  background-color: rgba(var(--header-bg), 0.9);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  padding: var(--space-2) 0;
}
[data-theme="dark"] .site-header.scrolled {
  background-color: rgba(15, 23, 42, 0.9);
}

.site-header .container { display: flex; justify-content: space-between; align-items: center; }
.logo { font-size: 1.5rem; font-weight: 800; color: var(--primary-color); letter-spacing: -0.05em; }

/* Nav */
.nav-menu { display: none; }
.nav-menu ul { display: flex; gap: var(--space-5); }
.nav-menu a { color: var(--text-color); font-weight: 500; }
.nav-menu a:hover { color: var(--primary-color); }
.menu-toggle { display: block; background: none; border: none; cursor: pointer; padding: var(--space-2); min-width: 44px; min-height: 44px; }
.menu-toggle .bar { display: block; width: 24px; height: 2px; margin: 5px auto; background-color: var(--text-color); transition: all 0.3s; }

.nav-menu.active {
  display: block; position: absolute; top: 100%; left: 0; width: 100%;
  background-color: var(--header-bg); border-bottom: 1px solid var(--border-color);
  padding: var(--space-4); box-shadow: var(--shadow-md);
}
.nav-menu.active ul { flex-direction: column; gap: var(--space-4); align-items: center; }

/* Hero Section */
.hero {
  padding: var(--space-8) 0 var(--space-6);
  text-align: center;
  background: radial-gradient(circle at top right, var(--panel-bg) 0%, transparent 70%);
}
.hero p {
  font-size: 1.25rem; color: var(--text-muted); max-width: 600px; margin: 0 auto;
}

/* Sections */
.tools-section { padding: var(--space-8) 0; }
.tools-grid { grid-template-columns: 1fr; }
.category-header { font-size: 1.25rem; font-weight: 700; color: var(--text-muted); text-transform: uppercase; letter-spacing: 0.05em; margin-bottom: var(--space-4); margin-top: var(--space-8); border-bottom: 2px solid var(--border-color); padding-bottom: var(--space-2); }

/* Breakpoints */
@media (min-width: 640px) { .tools-grid { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 768px) {
  h1 { font-size: 3.5rem; }
  .menu-toggle { display: none; }
  .nav-menu { display: block; }
  .nav-menu.active { position: static; width: auto; background: none; border: none; padding: 0; box-shadow: none; }
  .footer-content { flex-direction: row; justify-content: space-between; }
}
@media (min-width: 1024px) { .tools-grid { grid-template-columns: repeat(3, 1fr); } }

/* Tool Cards */
.tool-card {
  background-color: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: var(--space-6);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-sm);
}
.tool-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl);
  border-color: var(--primary-color);
}
.tool-card-icon {
  width: 48px; height: 48px; margin-bottom: var(--space-4); color: var(--primary-color); display: flex; align-items: center; justify-content: center;
}
.tool-card-icon svg { width: 100%; height: 100%; fill: currentColor; }
.tool-card-title { font-size: 1.25rem; margin-bottom: var(--space-2); }
.tool-card-desc { color: var(--text-muted); margin-bottom: var(--space-5); flex: 1; font-size: 0.95rem; }

/* Buttons */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: var(--space-2);
  padding: 0.75rem 1.5rem; background-color: var(--primary-color); color: white; min-height: 44px;
  border: none; border-radius: 8px; font-weight: 600; cursor: pointer;
  transition: all 0.2s; box-shadow: var(--shadow-sm);
}
.btn:hover { background-color: var(--primary-hover); transform: translateY(-1px); box-shadow: var(--shadow-md); color: white; }
.btn:active { transform: scale(0.98); }

.btn-outline {
  background-color: transparent; color: var(--primary-color); border: 2px solid var(--primary-color); box-shadow: none;
}
.btn-outline:hover { background-color: rgba(79, 70, 229, 0.1); color: var(--primary-hover); border-color: var(--primary-hover); box-shadow: none; }

/* Forms */
.form-group { margin-bottom: var(--space-5); }
.form-group label { display: block; font-weight: 600; margin-bottom: var(--space-2); color: var(--text-color); }
.input-field {
  width: 100%; padding: 0.75rem 1rem; border: 1px solid var(--border-color); border-radius: 8px; min-height: 44px;
  font-family: inherit; font-size: 1rem; background-color: var(--bg-color); color: var(--text-color);
  transition: all 0.2s; box-shadow: var(--shadow-sm);
}
textarea.input-field { resize: vertical; min-height: 200px; line-height: 1.5; }
.input-field:focus { outline: none; border-color: var(--primary-color); box-shadow: var(--focus-ring); }
input[type="range"] { padding: 0; box-shadow: none; min-height: 44px; }

/* Tool UI */
.tool-container {
  background-color: var(--card-bg); border: 1px solid var(--border-color); border-radius: 12px;
  padding: var(--space-5); margin: var(--space-6) 0; box-shadow: var(--shadow-md);
}
@media (min-width: 768px) { .tool-container { padding: var(--space-8); } }

.drop-zone {
  border: 2px dashed var(--border-color); border-radius: 12px; padding: var(--space-8) var(--space-4);
  text-align: center; background-color: var(--panel-bg); cursor: pointer; transition: all 0.2s; margin-bottom: var(--space-6);
}
.drop-zone:hover, .drop-zone.dragover { background-color: rgba(79, 70, 229, 0.05); border-color: var(--primary-color); }
.drop-zone-icon { width: 48px; height: 48px; margin: 0 auto var(--space-4); color: var(--primary-color); }
.drop-zone-text { font-size: 1.125rem; font-weight: 600; margin-bottom: var(--space-1); }
.drop-zone-sub { color: var(--text-muted); font-size: 0.875rem; }

/* Image Compressor specific */
.compression-workspace { display: none; gap: var(--space-6); flex-direction: column; }
@media (min-width: 768px) { .compression-workspace { flex-direction: row; } }
.image-preview-panel { flex: 1; border: 1px solid var(--border-color); border-radius: 12px; padding: var(--space-4); display: flex; flex-direction: column; align-items: center; background-color: var(--panel-bg); }
.image-preview-panel img { max-width: 100%; max-height: 350px; object-fit: contain; margin-bottom: var(--space-4); border-radius: 8px; box-shadow: var(--shadow-sm); }
.controls-panel { flex: 1; display: flex; flex-direction: column; gap: var(--space-5); }
.slider-container { display: flex; align-items: center; gap: var(--space-4); }

.savings-badge { display: inline-block; padding: 0.5rem 1rem; background-color: #dcfce7; color: #166534; border-radius: 8px; font-weight: 600; text-align: center; border: 1px solid #bbf7d0; }
.savings-badge.negative { background-color: #fee2e2; color: #991b1b; border-color: #fecaca; }

/* Article & FAQ */
.article-section {
  padding: var(--space-10) 0;
  max-width: 800px; margin: 0 auto;
}
.article-section h2 { margin-top: var(--space-8); padding-bottom: var(--space-2); border-bottom: 2px solid var(--border-color); }
.article-content { margin-bottom: var(--space-8); font-size: 1.1rem; }
.faq-list { display: flex; flex-direction: column; gap: var(--space-6); }
.faq-item h3 { font-size: 1.25rem; margin-bottom: var(--space-2); }

/* Stat Cards (Word Counter) */
.stats-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: var(--space-4); }
@media (min-width: 768px) { .stats-grid { grid-template-columns: repeat(3, 1fr); } }
.stat-card { background-color: var(--card-bg); border-radius: 12px; padding: var(--space-5); text-align: center; border: 1px solid var(--border-color); box-shadow: var(--shadow-sm); transition: transform 0.2s; }
.stat-card:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); }
.stat-value { font-size: 2.5rem; font-weight: 800; color: var(--primary-color); line-height: 1; margin-bottom: var(--space-2); letter-spacing: -0.05em; }

/* Toast */
.toast-container { position: fixed; bottom: var(--space-6); right: var(--space-6); z-index: 9999; display: flex; flex-direction: column; gap: var(--space-3); }
.toast { padding: 1rem 1.5rem; background-color: var(--card-bg); color: var(--text-color); border-left: 4px solid var(--primary-color); border-radius: 8px; box-shadow: var(--shadow-lg); animation: slideInRight 0.3s cubic-bezier(0.4, 0, 0.2, 1) forwards, fadeOut 0.3s ease 2.7s forwards; font-weight: 600; }
.toast.error { border-left-color: var(--error-color); }

@keyframes slideInRight { from { transform: translateX(100%); opacity: 0; } to { transform: translateX(0); opacity: 1; } }
@keyframes fadeOut { from { opacity: 1; } to { opacity: 0; } }
@keyframes fadeIn { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: translateY(0); } }
main { animation: fadeIn 0.4s ease forwards; }

.spinner { display: inline-block; width: 1.5rem; height: 1.5rem; border: 3px solid rgba(255,255,255,0.3); border-radius: 50%; border-top-color: #fff; animation: spin 1s linear infinite; vertical-align: middle; margin-right: 0.5rem; }
@keyframes spin { to { transform: rotate(360deg); } }

/* Ad Placeholders */
.ad-slot { width: 100%; min-height: 90px; border: 2px dashed var(--border-color); background-color: var(--panel-bg); color: var(--text-muted); display: flex; align-items: center; justify-content: center; margin: var(--space-8) 0; font-weight: 600; border-radius: 8px; }
.ad-slot.square { min-height: 250px; }

/* Print */
@media print {
  .site-header, .site-footer, .ad-slot, .related-tools-section, .btn, .menu-toggle, .nav-menu { display: none !important; }
  body { background: #fff; color: #000; }
  .tool-container { border: none; box-shadow: none; }
}

/* Footer */
.site-footer { background-color: var(--footer-bg); padding: var(--space-8) 0; margin-top: auto; border-top: 1px solid var(--border-color); }
.footer-content { display: flex; flex-direction: column; align-items: center; gap: var(--space-5); }
.footer-links { display: flex; gap: var(--space-4); flex-wrap: wrap; justify-content: center; }
.footer-links a { color: var(--text-muted); font-weight: 500; }
.footer-links a:hover { color: var(--primary-color); }

/* Theme Toggle Button */
.theme-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 8px;
  background-color: var(--panel-bg);
  color: var(--text-color);
  border: 1px solid var(--border-color);
  cursor: pointer;
  transition: all 0.2s;
  box-shadow: var(--shadow-sm);
  padding: 0;
}
.theme-btn:hover {
  background-color: var(--border-color);
  transform: scale(0.95);
}
.theme-btn svg {
  width: 20px;
  height: 20px;
  fill: currentColor;
}

/* Fallback for Tool Icons */
.tool-card-icon svg {
  width: 48px;
  height: 48px;
}