html,
body {
  width: 768px;
  margin: 0 auto;
  font-size: 16px;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  box-sizing: border-box;
}

body {
  padding: 0 1rem;
}

header {
  text-align: center;
}

#theme-btn {
  display: inline-block;
  background-color: transparent;
  margin: 1rem 0;
  border: 1px solid white;
  border-radius: 15%;
  height: 2.4rem;
  width: 2.4rem;
}

#theme-btn:hover {
  cursor: pointer;
}

nav {
  float: right;
}

#nav-list {
  margin: 1rem;
  padding: 0;
}

#nav-list li {
  height: 2.4rem;
  line-height: 2.4rem;
  display: inline-block;
  margin-right: 1rem;
  margin-left: 1rem;
  list-style-type: none;
}

#nav-list li a {
  text-decoration: none;
  font-size: 1.2rem;
}

#nav-list li a:hover {
  text-decoration: underline;
}

main {
  clear: both;
}

main article h2 {
  font-size: 1.8rem;
  margin: auto 0;
}

main article h3 {
  font-size: 1.6rem;
}

main article p {
  font-size: 1rem;
}

main article a {
  font-weight: bold;
  text-decoration: underline;
}

main article a:hover {
  color: lightsalmon;
}

article .wechat-qr {
  width: 200px;
  height: 200px;
  margin: 0 auto;
  display: block;
}

footer {
  border-top: 1px solid white;
}

footer p {
  text-align: center;
}

.theme-black {
  background-color: #020617;
  color: white;
}

.theme-white {
  background-color: white;
  color: #020617;
}

/*增加媒体查询，屏幕宽度小于768px时，body宽度100%*/
@media screen and (max-width: 768px) {
  html,
  body {
    width: 100%;
  }
}