Edit in JSFiddle

#dnn_dnnSEARCH_txtSearch {
  background: url(https://crmassistent.com/Portals/32-System/Skins/CRMAssistent/images/search-icon.png) no-repeat 9px center;
  -webkit-transition: all .5s;
  -moz-transition: all .5s;
  transition: all .5s;
  width: 0px;
  border-radius: 10em;
  -webkit-border-radius: 10em;
  -moz-border-radius: 10em;
  content: "";
  padding: 9px 10px 9px 32px;
  margin: 5px 0;
  border: none;
}

#dnn_dnnSEARCH_txtSearch:focus {
  width: 150px;
  cursor: pointer;
  border-radius: 10em;
  -webkit-border-radius: 10em;
  -moz-border-radius: 10em;
  -webkit-box-shadow: 0 0 3px #f5f5f5;
  -moz-box-shadow: 0 0 3px #f5f5f5;
  box-shadow: 0 0 3px #f5f5f5;
  outline:0;
  color: rgba(245, 245, 245, 0.75);
}

#dnn_dnnSEARCH_txtSearch input[type="placeholder"] {
  padding: 5px;
  font-style: normal!important;
  color: #000;
  font-size: 13px;
  content: ""
}

.searchInputContainer a.dnnSearchBoxClearText{
  display:none!important;
}

input[type="text"]{
  font-size: 13px;
  font-style: italic;
}