:root {
  --bg-color: #ffffff;
  --text-color: #222222;
  --link-color: #1a73e8;
}
body.dark {
  --bg-color: #121212;
  --text-color: #dddddd;
  --link-color: #90caf9;
}
body {
  margin: 0;
  font-family: "Segoe UI", sans-serif;
  background-color: var(--bg-color);
  color: var(--text-color);
  transition: background 0.3s, color 0.3s;
}
header {
  background: var(--link-color);
  color: #fff;
  padding: 1rem 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
}
nav a {
  margin: 0 1rem;
  color: white;
  text-decoration: none;
}
nav a:hover {
  text-decoration: underline;
}
nav img {
  height: 20px;
  vertical-align: middle;
  margin-left: 0.3rem;
}
.container {
  max-width: 800px;
  margin: auto;
  padding: 2rem 1rem;
}
section {
  margin-bottom: 2.5rem;
}
h1, h2 {
  color: var(--text-color);
}
a {
  color: var(--link-color);
}
footer {
  text-align: center;
  padding: 2rem 0;
  font-size: 0.9em;
  color: #aaa;
}
.toggle {
  cursor: pointer;
  font-size: 0.9em;
  padding: 0.4rem 0.6rem;
  background: #fff;
  border: none;
  border-radius: 4px;
  color: var(--link-color);
}

.card {
  border: 1px solid #ccc;
  padding: 1.2rem;
  margin-bottom: 1.5rem;
  border-radius: 8px;
  background: #f9f9f9;
  transition: box-shadow 0.3s ease-in-out;
}
.card:hover {
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}
.card h3 {
  margin-top: 0;
}