:root {
  --color-bg: #ffffff;
  --color-text: #222222;
  --color-primary: #0078d7;
  --color-secondary: #555555;
  --color-card-bg: #f9f9f9;
  --color-border: #ddd;
  --transition-speed: 0.3s;
}

[data-theme="dark"] {
  --color-bg: #121212;
  --color-text: #e1e1e1;
  --color-primary: #5599ff;
  --color-secondary: #bbb;
  --color-card-bg: #1e1e1e;
  --color-border: #333;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  transition: background-color var(--transition-speed),
    color var(--transition-speed);
}

header {
  padding: 1.5rem;
  background-color: var(--color-primary);
  color: white;
  text-align: center;
  position: relative;
}

header h1 {
  margin: 0;
  font-size: 2rem;
}

header p {
  margin: 0.25rem 0 0;
  font-weight: 400;
}

#toggleThemeBtn {
  position: absolute;
  right: 1rem;
  top: 1.5rem;
  background: transparent;
  border: 2px solid white;
  color: white;
  border-radius: 6px;
  padding: 0.25rem 0.75rem;
  cursor: pointer;
  font-size: 1.1rem;
  transition: background-color 0.3s ease;
}

#toggleThemeBtn:hover,
#toggleThemeBtn:focus {
  background-color: rgba(255, 255, 255, 0.2);
  outline: none;
}

main {
  display: flex;
  flex-wrap: wrap;
  max-width: 1200px;
  margin: 2rem auto;
  gap: 2rem;
  padding: 0 1rem;
}

.category-filters {
  text-align: center;
  margin: 1rem auto 0.5rem;
  width: 100%;
  max-width: 800px;
}

.filter-btn {
  background-color: var(--color-card-bg);
  border: 1.5px solid var(--color-border);
  color: var(--color-text);
  margin: 0 0.25rem 0.5rem;
  padding: 0.4rem 1rem;
  border-radius: 20px;
  cursor: pointer;
  font-weight: 600;
  transition: background-color 0.3s ease, border-color 0.3s ease;
}

.filter-btn:hover,
.filter-btn:focus {
  border-color: var(--color-primary);
  outline: none;
}

.filter-btn.active {
  background-color: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.search-bar {
  max-width: 600px;
  margin: 1rem auto 2rem;
  padding: 0 1rem;
  text-align: center;
  width: 100%;
}

#groupSearch {
  width: 100%;
  max-width: 600px;
  padding: 0.5rem 1rem;
  font-size: 1rem;
  border-radius: 8px;
  border: 1.5px solid var(--color-border);
  transition: border-color 0.3s ease;
}

#groupSearch:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 5px var(--color-primary);
}

.groups {
  flex: 3 1 600px;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.group-card {
  background-color: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: 10px;
  padding: 1rem 1.25rem;
  box-shadow: 0 2px 5px rgb(0 0 0 / 0.05);
  transition: box-shadow 0.3s ease;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  position: relative;
}

.group-card:hover,
.group-card:focus-within {
  box-shadow: 0 5px 15px rgb(0 0 0 / 0.15);
  outline: none;
}

.group-card h3 {
  margin: 0 0 0.5rem;
  font-size: 1.25rem;
  color: var(--color-primary);
}

.group-card p {
  flex-grow: 1;
  margin: 0 0 0.75rem;
  color: var(--color-secondary);
}

.group-card .members {
  font-weight: 600;
  margin-bottom: 0.75rem;
}

.group-card a {
  text-decoration: none;
  color: white;
  background-color: var(--color-primary);
  padding: 0.5rem 1rem;
  border-radius: 6px;
  text-align: center;
  font-weight: 600;
  transition: background-color 0.3s ease;
  align-self: flex-start;
}

.group-card a:hover,
.group-card a:focus {
  background-color: #005ea6;
  outline: none;
}

.qr-btn {
  background-color: var(--color-primary);
  border: none;
  color: white;
  padding: 0.4rem 0.8rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  margin-top: 0.5rem;
  align-self: flex-start;
  transition: background-color 0.3s ease;
}

.qr-btn:hover,
.qr-btn:focus {
  background-color: #005ea6;
  outline: none;
}

.qr-code {
  margin-top: 0.75rem;
  width: 130px;
  height: 130px;
  display: flex;
  justify-content: center;
  align-items: center;
}

.stats {
  flex: 1 1 280px;
  background-color: var(--color-card-bg);
  border: 1px solid var(--color-border);
  border-radius: 10px;
  padding: 1rem 1.5rem;
  height: fit-content;
  box-shadow: 0 2px 8px rgb(0 0 0 / 0.05);
}

.stats h2 {
  margin-top: 0;
  color: var(--color-primary);
  font-size: 1.5rem;
}

.stats ul {
  list-style: none;
  padding-left: 0;
  font-size: 1.1rem;
  color: var(--color-text);
}

.stats li {
  margin: 0.75rem 0;
}

.loading {
  font-style: italic;
  color: var(--color-secondary);
  text-align: center;
}

footer {
  text-align: center;
  padding: 1rem 1rem;
  background-color: var(--color-primary);
  color: white;
  font-size: 0.9rem;
  margin-top: 3rem;
}

/* Responsive tweaks */

@media (max-width: 768px) {
  main {
    flex-direction: column;
  }
  .groups {
    grid-template-columns: 1fr;
  }
  .stats {
    margin-top: 2rem;
  }
}