*{margin: 0; padding: 0;}
body {background: #f4f3f3;; font-family:"Open Sans",sans-serif; ; font-size: 12px}
.contenedor { margin: 0 auto; width: 960px; height: 600px;padding: 50px; }
h1 {font-family:"Open Sans",sans-serif; font-weight: 300;font-size: 40px; margin: 5px;}
h2 {font-family:"Open Sans",sans-serif; font-weight: 200 ;font-size: 20px; color:#878787}
h3 {font-family: "Open Sans",sans-serif;font-weight: 500;font-size: 12px;color: #000;}
a {text-decoration: none;}
p {font-family:"Open Sans",sans-serif; font-weight: 100 ;font-size: 12px}

<!--header!-->

header {background-color: #fff; height: 210px; width: 100%; padding-bottom: 20px}
.header_img { width: 75%; position: relative ; float: left;}
header nav ul {display: inline; list-style-type: none;}
header nav ul li{text-decoration: none;background-color: #F01042;margin: 10px;color: #FFF;height: 25px;padding: 5px 5px 0 0;text-align: center;width: 150px;font-size: 15px;}


nav { width: 25%; position: relative ; float: right; text-align: right;
font-size: 25px;}

<!--main!-->
main {width: 100%; position: relative ; float: left;}

section {margin-top:10px; }
.materias {position: relative; float: left;width: 45%;padding: 15px; border: 1px solid #B2B2B2}
.facu { width: 45%;height: 250px;position: relative;float: right;padding: 0 25px;}

<!--footer!-->
.clear {clear: both;}
footer {text-align:left;position: relative;float:left; width:100%;height: "30px"; padding-top: 10px;background:#C4C5C6; width: 100%; padding: 10px; }
.info_footer {width: 980px; height: 100%;margin: 0 auto;}