html {
  font-family: "Lucida Sans", sans-serif;
  background-color: #000;
  color: #bbb;
}
.menu li {
  padding: 8px;
  margin-bottom: 7px;
  background-color: #333;
  color: #ffffff;
  box-shadow: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
}
.menu li:hover {
  color: #fff;
  background-color: #666;
}
#html-btn,
#epub-btn,
#pdf-btn {
  border: 2px;
  color: #333;
  background-color: #000;
  padding: 13px 13px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 24px;
}