.bg {
  background: url(../images/mobail_bg2.png) no-repeat;
  background-size: 100% 100%;
}
.nav_bg {
  background: url(../images/nav_bg.png) no-repeat;
  background-size: 100% 100%;
}
.nav {
  width: 80%;
  margin: 0 auto;
  overflow: hidden;
  list-style: none;
}
.nav li {
  float: left;
  margin-top: 30px;
  width: 25%;
}
.nav li img {
  width: 50%;
}