* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0;
  background-color: #FBF8FE;

  /* text responsiveness */

  font-size: clamp(16px, 2.5vw, 18px);
  line-height: 1.6;
  padding: 10px;
  text-align: center
}
	

  
h1 {
  color:  #33194B ;
  text-align: center;
}
h2 {
  color:#C7BAD4   ;
  text-align: center;
}
img {
  width: 500px;  /* sets width to 300px */
  height: auto;  /* keeps aspect ratio */
    border-radius: 20px;
	border: 5px solid #33194B;
}


header {
  background-image: url("headerozadje2.jpg");
   background-size: cover; 
  padding: 20px;
  text-align: center;
  color: #33194B;
  width: 100%;
position: sticky;       /* keeps it visible when scrolling */
  top: 0;                    /* sticks to the top */
  z-index: 1000;
  text-shadow: 3px 3px white;
   
}

/* Style the topnav */
ul.topnav {
  display: flex;
  list-style-type: none;
  margin: 0;
  padding: 0;
  background-color: #33194B;
  width: 100%;
  position: sticky;
   top: 100 ;                    /* sticks to the top */
  z-index: 1000;
}

/* Style links in topnav */
ul.topnav li a {
  display: block;
  color: #ffffff;
  padding: 14px 16px;
  text-decoration: none;
}

/* Change color on hover */
ul.topnav li a:hover {
  background-color:#ffffff ;
  color:#33194B ;
}
<ul class="topnav">
 <li><a href="index.html">Domov</a></li>
  <li><a href="erasmus1/erasmus1.html">Splošno</a></li>
  <li><a href="erasmus2/erasmus2.html">Spolni stereotipi</a></li>
  <li><a href="erasmus3/erasmus3.html">Izmenjava</a></li>
  <li><a href="erasmus4/erasmus4.html">Okrogla miza</a></li>
</ul>