body {
  font-family: system-ui, Arial, sans-serif;
  margin: 0;
  background: #f7f8fa;
  color: #232323;
}
header {
  background: #232b36;
  color: #fff;
  padding: 1rem 2rem;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}
header h1 {
  margin: 0 0 0.5rem 0;
}
nav {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
  align-items: center;
}
nav a {
  color: #fff;
  text-decoration: none;
  font-weight: 500;
}
nav a.active, nav a:hover {
  text-decoration: underline;
}
nav span, nav button {
  margin-left: 1rem;
}
main#app {
  max-width: 900px;
  margin: 2rem auto;
  background: #fff;
  padding: 2rem;
  min-height: 60vh;
  border-radius: 7px;
  box-shadow: 0 1px 8px rgba(30,50,100,0.07);
}
footer {
  text-align: center;
  padding: 2rem 0 1rem 0;
  color: #999;
}
button {
  background: #4285f4;
  color: #fff;
  border: none;
  border-radius: 3px;
  padding: 0.5rem 1.2rem;
  cursor: pointer;
  font-size: 1rem;
  margin-left: 0.5rem;
}
button:hover {
  background: #3367d6;
}
@media (max-width: 600px) {
  main#app { padding: 1rem; }
  header { padding: 1rem; }
}