Why 100vh is not taking the full screen?

This is the first time I'm getting this type of problem. I'm trying to make responsive navigation bar. At a certain width, I want my nav links div to go to right side bar. But the nav links div is not taking full viewport height even after giving 100vh. Here is the code -

HTML

<header>
  <nav>
    <div class="logo">Logo</div>

    <div class="nav-items">
      <li><a href = '#'>Link-1</a></li>
      <li><a href = '#'>Link-2</a></li>
      <li><a href = '#'>Link-3</a></li>
    </div>
  </nav>
</header>

SCSS

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

header {
  background: blue;
    nav {
        height: 65px;
        max-width: 1340px;
        width: 100%;
        display: flex;
        justify-content: space-between;
        align-items: center;
        margin: auto;
        padding: 1rem;

        .logo {
            font-size: 2rem;
            color: black;
        }

        .nav-items {
            li {
                display: inline;

                a {
                    color: black;
                    text-decoration: none;
                    margin-left: 2rem;
                }
            }
        }

    }
}

@media screen and (max-width: 768px) {    
    header nav .nav-items {
        position: absolute;
        right: 0;
        height: 100vh;
        width: 50%;
        border: 1px solid black;
    }
}

Link to codepen -

https://codepen.io/yell0wflash/pen/JjWGwJa

Set position to fixed, add top:0; also height:100vh and left or right to 0 in the media query