* {
  font-size: 16px;
}

header {
  position: fixed;
  width: 100%;
  height: 4rem;
  left: 0;
  top: 0;
  z-index: 30;
  background-color: rgba(0, 0, 0, 0.8);
  padding-left: 2.5rem;
  display: flex;
  align-items: center;
  box-sizing: border-box;
  transition: background-color 0.3s;
}

.logo {
  height: 3rem;
}

.nav {
  display: flex;
  list-style-type: none;
  margin-left: 2rem;
}

.nav-item {
  margin: 0 0.5rem;
}

.nav .nav-item a {
  display: block;
  padding: 0.5rem 1rem;
  text-decoration: none;
  color: #fff;
  border-radius: 4px;
  transition: background-color 0.3s, color 0.3s;
}

.nav .nav-item a.active {
  background-color: #009688;
  color: #fff;
}

.nav .nav-item a:hover {
  background-color: #007a6e;
  color: #fff;
}

.header-extra {
  margin-left: auto;
  margin-right: 2.5rem;
}

.header-extra .btn {
  width: 7rem;
  height: 2.2rem;
  font-size: 0.9rem;
  background-color: #009688;
  border: none;
  color: white;
  border-radius: 4px;
  cursor: pointer;
  transition: background-color 0.3s;
}

.header-extra .btn:hover {
  background-color: #007a6e;
}