<div class="searchbox">
  <input id="searchInput" onkeypress="zoekArtikel(event);" type="text">
</div>

.searchbox{
    width:265px;
    height: 37px;
    background-color: #000d59;
    margin-left:40px;
    margin-top:90px;
}

#searchInput{
    width:203px;
    margin-left:10px;
    margin-right:10px;
    margin-top:7px;
    height:20px;
    -moz-border-radius:28px; /* makes no differnce */
    border-radius:28px;
    padding-left:5px;
    padding-right:35px;
    background-size: 25px 20px;
}