Div qui occupe 100% de la hauteur du div parent

html {
 height: 100%;
 width: 100%;
}

body {
 height: 100%;
 width: 100%;
 max-width: 100%;
}

li {
 padding:0% 2% 0% 2%;
 display: inline-block;
}

ul {
 text-align: center;
 display: inline-block;
 padding:0;
 margin:0;
 width: 79%;
}

header {
 background-color: #1397A3;
}

@font-face{
 font-family: 'CaviarDreams';
 src:url('font/CaviarDreams.ttf');
}

a {
 font-family: CaviarDreams;
 text-decoration: none;
 color: #fff;
}

header nav img {
 width: 20%;
}

<header>
 <nav>
 <img src="logo.png" alt="logo" />  
 
  <ul>
   <li><a href="index.html">Home</a></li>
   <li><a href="portfolio.php">Portfolio</a></li>
   <li><a href="cv.php">CV</a></li>
   <li><a href="contact.php">Contat</a></li>
  </ul>   
 </nav>

</header>