HTML Datalist won't restrict to 5 or x items to be visible with a scroll

Question

I tried to no avail to get HTML, CSS and Javascript to limit number of items in datalist, for whatever reason, it is isn't working. The list is populated by a loop on a array.

<datalist id="trainNoList">
 <script>
if (markers)
{
  var options = '';
  var trainNoList = [];
  

  for (var i = 0; i < markers.length; i++) {
    var trainNo = markers[i][20];
    trainNoList.push(trainNo);
    options += "<option value='" + trainNoList[i] + "'></option>";
  }

}
</script>
</datalist>

<!-- Use JavaScript to pan to the train when an option is selected -->

<script>
  $("#trainNoInput").on("input", function() {
    var selectedTrainNo = $(this).val();
    
    // Check if the input is a range
    var rangeCheck = selectedTrainNo.split("-");
    if (rangeCheck.length === 2) {
      vehiclestart = rangeCheck[0];
      vehicleend = rangeCheck[1];
      
    } else {
      // Perform the same actions as in the original code
      for (var i = 0; i < markers.length; i++) {
        var trainNo = markers[i][20]; 
        if (trainNo == selectedTrainNo) {
          var lat = parseFloat(markers[i][2]);
          var lng = parseFloat(markers[i][3]);
          var setcontentforpopup = "Vehicle"+markers[i][0]+"";
            vehiclestart = 1;
      vehicleend = 99999999999999;
          var popup = L.popup()
            .setLatLng([lat, lng])
            .setContent(setcontentforpopup)
            .addTo(map);
          map.flyTo([lat, lng], 16);
          break;
        }
      }
    }
  });
  
$("#trainNoInput").on("focus", function() {
    console.debug("The trainNoInput field has received a keyup event");
clearTimeout(ajaxtimeout);
});

$("#trainNoInput").on("blur", function() {
ajaxtimeout = setTimeout(foo, 10000);
console.debug("no");
});

$("#trainNoInput").on("keyup", function(event) {
if (event.keyCode === 13) {
    markerLookup = {};
     markerClusters.clearLayers();
foo();
}
});


</script>

enter image description here

The desire result is simple - limit number of items shown down to 5 or whatever set amount and add a scroll bar to scroll down to see the remainder of the records

enter image description here