/* Base */
* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

html, body {
  overflow-x: hidden;
}

body {
  font-family: Georgia, "Times New Roman", serif;
  max-width: 1100px;
  margin: 0 auto;
  padding: 48px 32px;
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
  transition: background 0.25s ease, color 0.25s ease;
}

/* Dark mode variables */
:root {
  --bg: #ffffff;
  --text: #202124;
  --muted: #6b6b6b;
  --border: #e0e0e0;
  --link: #0645ad;
  --link-hover-bg: #e8f0fe;
  --badge-bg: #e7f4fa;
  --badge-border: #b7d7e8;
  --badge-text: #2274a5;
  --toc-bg: #fafbfc;
  --footer-bg: #f8f9fa;
  --footer-border: #dcdcdc;
  --input-bg: #ffffff;
  --input-border: #a0a0a0;
  --input-focus-border: #2274a5;
  --card-bg: #ffffff;
  --header-bg: #ffffff;
}

[data-theme="dark"] {
  --bg: #121212;
  --text: #e5e5e5;
  --muted: #9aa0a6;
  --border: #2c2c2c;
  --link: #8ab4f8;
  --link-hover-bg: rgba(138, 180, 248, 0.18);
  --badge-bg: #1e2a3a;
  --badge-border: #3a4b63;
  --badge-text: #bcd6ff;
  --toc-bg: #1b1b1b;
  --footer-bg: #141414;
  --footer-border: #2c2c2c;
  --input-bg: #1a1a1a;
  --input-border: #3a3a3a;
  --input-focus-border: #8ab4f8;
  --card-bg: #171717;
  --header-bg: #171717;
}

/* Headings */
h1 {
  font-size: 2.8rem;
  font-weight: normal;
  text-align: center;
  margin-bottom: 48px;
  border-bottom: 1px solid var(--border);
  padding-bottom: 20px;
}

h2 {
  font-size: 1.8rem;
  font-weight: normal;
  margin-top: 48px;
  border-bottom: 1px solid var(--border);
  padding-bottom: 6px;
}

h3 {
  font-size: 1.2rem;
  font-weight: normal;
  margin-top: 32px;
  margin-bottom: 12px;
}

/* Course section */
.course {
  margin-bottom: 48px;
  border-bottom: 1px solid var(--border);
  padding-bottom: 2rem;
}

/* Topics */
.topic {
  margin-bottom: 1.5rem;
  padding-left: 16px;
  border-left: 3px solid var(--border);
}

.topic:last-child {
  border-left: none;
}

/* Resource list */
.resources {
  padding-left: 28px;
  margin: 0;
}

.resources li {
  margin-bottom: 6px;
  font-size: 0.95rem;
}

/* Links */
a {
  color: var(--link);
  text-decoration: none;
  transition: background 0.2s ease, color 0.2s ease;
  position: relative;
  padding: 0 2px;
  border-radius: 3px;
}

a:hover {
  background-color: var(--link-hover-bg);
  text-decoration: underline;
}

/* Tooltip showing full URL */
a::after {
  content: attr(href);
  position: absolute;
  left: 50%;
  bottom: 125%;
  transform: translateX(-50%);
  background: rgba(0, 0, 0, 0.75);
  color: #fff;
  font-size: 0.75rem;
  padding: 4px 8px;
  border-radius: 4px;
  white-space: nowrap;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s ease;
  z-index: 10;
}

a:hover::after {
  opacity: 1;
}

/* Collapsible toggles */
.collapsible-toggle {
  background: none;
  border: none;
  cursor: pointer;
  font-size: 0.9rem;
  opacity: 0.6;
  transition: transform 0.2s ease, opacity 0.2s ease;
}

.collapsible-toggle:hover {
  opacity: 1;
}

.topic.collapsed > ul,
.topic.collapsed > .resources {
  display: none;
}

/* Badges */
.resource-badge {
  font-size: 0.75rem;
  opacity: 0.7;
  margin-left: 0.4rem;
  vertical-align: middle;
  background: var(--badge-bg);
  color: var(--badge-text);
  border: 1px solid var(--badge-border);
  padding: 0.13em 0.7em;
  border-radius: 999px;
}

/* Layout */
main {
  display: flex;
  gap: 2.5rem;
  align-items: flex-start;
}

.main-content {
  flex: 1;
  min-width: 0;
}

/* Sticky Table of Contents */
.toc-sticky {
  position: sticky;
  top: 1rem;
  max-width: 320px;
  background: var(--toc-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1rem;
  margin-bottom: 2rem;
}

/* Responsive */
@media (max-width: 900px) {
  main {
    flex-direction: column;
  }
  .toc-sticky {
    position: relative;
    top: auto;
    max-width: 100%;
  }
}

/* Search input */
#search {
  width: 100%;
  max-width: 400px;
  padding: 0.6em 1.2em;
  font-size: 1.1rem;
  border: 1.5px solid var(--input-border);
  border-radius: 24px;
  margin: 1.5em 0 2em 0;
  box-shadow: inset 0 1px 3px rgba(0,0,0,0.1);
  background: var(--input-bg);
  color: var(--text);
}

#search:focus {
  border: 2px solid var(--input-focus-border);
  outline: none;
  box-shadow: 0 0 5px rgba(34, 116, 165, 0.3);
}

/* Back to top */
#backToTop {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  padding: 0.6em 1em;
  font-size: 1.2rem;
  border: none;
  background: #2274a5;
  color: #fff;
  border-radius: 6px;
  cursor: pointer;
  display: none;
}

#backToTop:hover {
  background: #135c84;
}

/* Footer */
footer {
  background-color: var(--footer-bg);
  color: var(--text);
  padding: 2.5rem 1.5rem;
  margin-top: 4rem;
  border-top: 1px solid var(--footer-border);
  font-size: 0.95rem;
  line-height: 1.6;
}

footer .footer-container {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 2rem;
  max-width: 1100px;
  margin: 0 auto;
}

footer .footer-column h4 {
  font-weight: bold;
  margin-bottom: 0.75rem;
  font-size: 1.05rem;
}

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

footer .footer-column li {
  margin-bottom: 0.5rem;
}

footer a {
  color: var(--link);
  text-decoration: none;
}

footer a:hover {
  text-decoration: underline;
}

/* Theme toggle button */
/* Theme toggle button */
#themeToggle,
#randomArticle,
#learningFramework,
#openGraph {
  position: fixed;
  top: 18px;
  z-index: 999;
  padding: 8px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--toc-bg);
  color: var(--text);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 0.95rem;
  cursor: pointer;
  transition: background 0.2s ease, border-color 0.2s ease, transform 0.1s ease;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
}

#themeToggle {
  left: 18px;
}

#randomArticle {
  left: 140px;
}

#learningFramework {
  left: 270px;
}

#learningFramework{
  left: 300px;
}

#themeToggle:hover,
#randomArticle:hover,
#learningFramework:hover
 {
  background: var(--badge-bg);
  border-color: var(--badge-border);
}

#themeToggle:active,
#randomArticle:active,
#learningFramework:active,
#openGraph:active {
  transform: translateY(1px);
}

/* Responsive */
@media (max-width: 700px) {
  body {
    padding: 24px 16px;
  }

  #themeToggle {
    top: 12px;
    left: 12px;
    padding: 7px 10px;
    font-size: 0.9rem;
  }

  #randomArticle,
  #learningFramework,
   #learningFramework{
    left: 12px;
    right: auto;
    width: auto;
    top: auto;
  }

  #randomArticle {
    top: 54px;
  }

  #learningFramework {
    top: 100px;
  }
}

/* Header */
.site-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
  background: var(--header-bg);
}

.site-title {
  font-family: "Georgia", "Times New Roman", serif;
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  margin: 0;
}

.header-controls {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.search-wrap {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 6px 10px;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--card-bg);
}

.search-wrap input[type="search"] {
  border: none;
  outline: none;
  background: transparent;
  color: var(--text);
  width: 240px;
  font-size: 14px;
}

.search-wrap input[type="search"]::placeholder {
  color: var(--muted);
}

.search-icon {
  font-size: 14px;
  opacity: 0.7;
}

.filters {
  display: flex;
  gap: 12px;
  margin-bottom: 1rem;
}

.filters select {
  padding: 8px 12px;
  border-radius: 10px;
  border: 1px solid var(--input-border);
  background: var(--input-bg);
  color: var(--text);
}

/* Bookmark button */
.bookmark-btn,
.resource-bookmark-btn {
  margin-left: 10px;
  padding: 4px 8px;
  border-radius: 999px;
  border: 1px solid var(--badge-border);
  background: var(--badge-bg);
  color: var(--badge-text);
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s ease, border-color 0.2s ease, transform 0.1s ease;
}

.bookmark-btn:hover,
.resource-bookmark-btn:hover {
  background: var(--badge-text);
  color: var(--bg);
  border-color: var(--badge-text);
}

.bookmark-btn.saved,
.resource-bookmark-btn.saved {
  background: var(--badge-text);
  color: var(--bg);
  border-color: var(--badge-text);
}