html - 导航没有正确 float

Question

我试图将主要内容定位在左侧，将导航定位在右侧。目前导航位于底部。谁能告诉我哪里出错了？

代码(http://codepen.io/kiddigit/pen/PNXRVE)

* {
  font-family: garamond;
  line-height: 1.9em;
  color: #212121;
}
.wrapper {
  width: 75%;
  margin: 0 auto;
  border: 1px solid blue;
  padding: 10px;
  overflow: hidden;
}
.wrapper2{
  overflow: scroll;
}
.main_content {
  float: left;
}
.main_text {
  float: left;
}
.nav {
  float: right;
  padding-top: 10px;
  width: 25%;
}
header {
  border-bottom: 5px solid;
  margin-bottom: 10px;
  overflow: hidden;
}
header ul {
  list-style-type: none;
  margin-top: 20px;
  display: inline;
}
header li {
  float: right;
  margin-right: 20px;
  width: 110px;
}
header li:first-child { 
  margin-right: 0;
}
header li a {
  display: block;
  color: black;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}
header li a:hover {
  background-color: #111;
  color: white;
}
header h1 {
  float: left;
  text-align: left;
  margin: 0 170px .5em 0;
  line-height: 0;
  font-size: 2em;
}
h1 a {
  text-decoration: none;
  color: black;
}

/*drop-down menu styles begin*/
.dropbtn {
  color: black;
  padding: 13px;
  font-size: 16px;
  border: none;
  cursor: pointer;
}
.dropdown {
  display: inline-block;
  float: right;
}
.dropdown-content {
  display: none;
  position: absolute;
}
.dropdown-content a {
  color: white;
  padding: 0 27.5px ; 
  text-decoration: none;
  display: block;
  background-color: #3f3f3f;
}
.dropdown-content a:hover {
  color: #a9a9a9;
}
.dropdown:hover .dropdown-content {
  display: block;
}
.dropdown:hover .dropbtn {
  background-color: black;
  color: white;
}
/*drop-down menu styles end*/

/*Right nav content starts here*/
.nav li {
  list-style-type:none;
  font-size: 1em;
}
.nav ul {   
  padding-left: 10%;
  font-size: 1em;
}
.nav ul a:link {
  text-decoration: none;
  color: black;
  font-size: 1em;
}
.nav ul a:visited {
  text-decoration: none;
  color: black;
  font-size: 1em;
}
.nav ul a:hover {
  text-decoration: none;
  background-color: black;
  color: white;
  padding:3px;
  font-size: 1em;
}
/*Right nav ends here*/

Answer 1

将 width: 75%; 添加到 .main_content。它是一个 div，因此默认情况下它将占据其父容器的 100%。