.bg {
  background: url(../images/bg.png) repeat;
  height: 100%;
}
html,body {
  height: 100%;
}
.main {
  width: 90%;
  margin: 0 auto;
}
.introduce-text {
  width: 80%;
  padding: 20px 25px;
  position: relative;
  line-height: 1.5;
  text-align: justify;
  margin: 0 auto;
  font-size: 1.2em;
}
.top_left {
  position: absolute;
  left: 0;
  top: 0;
}
.top_right {
  position: absolute;
  right: 0;
  top: 0;
}
.bottom_left {
  position: absolute;
  bottom: 0;
  left: 0;
}
.bottom_right {
  position: absolute;
  bottom: 0;
  right: 0;
}