/* Enable smooth scrolling for in-page navigation */
html {
  scroll-behavior: smooth;
}

/* Dark theme variables */
:root {
  --bg-color: #121212;
  --surface-color: #1e1e1e;
  --accent-color: #bb86fc;
  --text-color: #e0e0e0;
  --muted-text-color: #a0a0a0;
  --max-width: 960px;
  --gap: 1.5rem;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  background-color: var(--bg-color);
  /* Page background image */
  background-image: url('background.png');
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
  background-attachment: fixed;
  color: var(--text-color);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,
    Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
  line-height: 1.6;
}

header {
  background-color: var(--surface-color);
  padding: 2rem 1rem;
  text-align: center;
}

nav ul {
  display: flex;
  justify-content: center;
  gap: var(--gap);
  list-style: none;
}

nav a {
  color: var(--text-color);
  text-decoration: none;
  font-weight: 500;
}

nav a:hover {
  color: var(--accent-color);
}

h1 {
  font-size: 2.5rem;
  margin-top: 1rem;
}

h2 {
  font-size: 2rem;
  margin-bottom: var(--gap);
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--muted-text-color);
}

main {
  padding: var(--gap) 1rem;
}

section {
  max-width: var(--max-width);
  margin: 0 auto var(--gap);
}

section#projects ul,
section#research ul {
  list-style: none;
  padding: 0;
}

section#projects li,
section#research li {
  margin-bottom: 0.75rem;
}

/* 3D model display container */
.model-gallery {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: var(--gap);
}

.model-container {
  background-color: var(--surface-color);
  border-radius: 8px;
  padding: 1rem;
  position: relative;
  width: 100%;
  height: 400px;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Footer styling */
footer {
  background-color: var(--surface-color);
  text-align: center;
  padding: 2rem 1rem;
}

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

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

/* Light theme overrides */
.light-theme {
  --bg-color: #f5f5f5;
  --surface-color: #ffffff;
  --accent-color: #007acc;
  --text-color: #1a1a1a;
  --muted-text-color: #555555;
}

/* Accessibility: focus styles */
nav a:focus-visible,
button#theme-toggle:focus-visible {
  outline: 2px solid var(--accent-color);
  outline-offset: 2px;
}

button#back-to-top:focus-visible {
  outline: 2px solid var(--accent-color);
  outline-offset: 2px;
}

/* Back-to-top button styling */
#back-to-top {
  position: fixed;
  bottom: 1rem;
  right: 1rem;
  width: 3rem;
  height: 3rem;
  background-color: var(--surface-color);
  color: var(--accent-color);
  border: none;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
  line-height: 1;
  font-size: 1.5rem;
  cursor: pointer;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
  z-index: 1000;
  opacity: 0.8;
  transition: background-color 0.3s ease, color 0.3s ease, opacity 0.3s ease;
}

#back-to-top:hover {
  background-color: var(--accent-color);
  color: var(--surface-color);
  opacity: 1;
}

/* Light mode section divider override */
body.light-theme h2 {
  border-bottom: 2px solid var(--text-color);
}

/* Wrap nav items on small screens */
@media (max-width: 600px) {
  nav ul {
    flex-wrap: wrap;
    gap: 0.75rem;
  }
}

/* Theme toggle button */
button#theme-toggle {
  position: fixed;
  top: 1rem;
  left: 1rem;
  width: 2.5rem;
  height: 2.5rem;
  background-color: var(--surface-color);
  color: var(--text-color);
  border: 2px solid var(--accent-color);
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
  font-size: 1rem;
  text-indent: -9999px;
  cursor: pointer;
  box-shadow: 0 2px 4px rgba(0,0,0,0.2);
  transition: background-color 0.3s ease, color 0.3s ease, transform 0.1s ease;
  z-index: 1000;
}
button#theme-toggle::before {
  content: "🌙";
  text-indent: 0;
}
.light-theme button#theme-toggle::before {
  content: "☀️";
}
button#theme-toggle:hover {
  background-color: var(--accent-color);
  color: var(--surface-color);
}
button#theme-toggle:active {
  transform: scale(0.95);
}

/* News section list styling */
#news ul {
  list-style-type: disc;
  list-style-position: outside;
  margin-top: 0.5rem;
  padding-left: 1.5rem;
}

/* News & Updates collapsible items */
#news ul li.hidden {
  display: none;
}

/* Show/hide button for News & Updates */
#news-toggle {
  display: none;
  margin-top: var(--gap);
  background-color: var(--surface-color);
  color: var(--text-color);
  border: 1px solid var(--accent-color);
  padding: 0.5rem 1rem;
  border-radius: 4px;
  cursor: pointer;
  transition: background-color 0.3s ease, color 0.3s ease;
}
#news-toggle:hover {
  background-color: var(--accent-color);
  color: var(--surface-color);
}