<div id="wrap">
  <header id="header"></header>
  <nav id="nav"></nav>
  <main id="main">
    <aside id="aside"></aside>
    <article id="article"></article>
    <section id="section"></section>
  </main>
  <div id="footer"></div>
</div>

* {
  margin: 0;
}
body {
  background-color: #E8F5E9;
}
#wrap {
  width: 1200px;
  margin: 0 auto;
}
#header {
  height: 100px;
  background-color: #C8E6C9;
}
#nav {
  height: 100px;
  background-color: #A5D6A7;
}
#main {
  display: flex;
}
#aside {
  width: 30%;
  height: 780px;
  background-color: #81C784;
}
#article {
  width: 40%;
  height: 780px;
  background-color: #66BB6A;
}

#section {
  width: 30%;
  height: 780px;
  background-color: #4CAF50;
}
#footer {
  height: 100px;
  background-color: #43A047;
}
/* 미디어 쿼리 */
@media( max-width : 1300px ){
  #wrap {
    width: 96%;
  }
}
@media( max-width : 768px ){
  #wrap {
    width: 100%;
  }
  #main {
    flex-wrap: wrap;
  }
  #aside {
    width: 30%;
    height: 630px;   
  }
  #article {
    width: 70%;
    height: 630px;
  }
  #section {
    width: 100%;
    height: 150px; 
  }
}
@media( max-width : 480px ){
  #aside {
    width: 100%;
    height: 200px;   
  }
  #article {
    width: 100%;
    height: 430px;
  }
}