.special {
  font-weight: bold !important;
  color: #fff !important;
  background: #bc0000 !important;
  text-transform: uppercase;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link href="https://stackpath.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<link href="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.9/dist/css/bootstrap-select.min.css" rel="stylesheet" />
<script src="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.9/dist/js/bootstrap-select.min.js"></script>

<select class="selectpicker">
  <option>Mustard</option>
  <option class="special">Ketchup</option>
  <option style="background: #5cb85c; color: #fff;">Relish</option>
</select>

$(function() {
  var $select = $('.select2');
  
  $select.select2({
    theme: 'paper'
  });
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.7/js/select2.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.7/css/select2.min.css" rel="stylesheet"/>

<select class="select2 form-control" placeholder="Country">
  <optgroup label="Alaskan/Hawaiian Time Zone">
    <option value="AK">Alaska</option>
    <option value="HI">Hawaii</option>
  </optgroup>
  <optgroup label="Pacific Time Zone">
    <option value="CA">California</option>
    <option value="NV">Nevada</option>
    <option value="OR">Oregon</option>
    <option value="WA">Washington</option>
  </optgroup>
</select>

$(function() {
  var $select = $('.select2');
  
  $select.select2({
    theme: 'paper'
  });
});

<link href="https://cdnjs.cloudflare.com/ajax/libs/bootswatch/3.3.2/paper/bootstrap.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.7/js/select2.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.7/css/select2.min.css" rel="stylesheet"/>

<select class="select2 form-control" placeholder="Country">
  <optgroup label="Alaskan/Hawaiian Time Zone">
    <option value="AK">Alaska</option>
    <option value="HI">Hawaii</option>
  </optgroup>
  <optgroup label="Pacific Time Zone">
    <option value="CA">California</option>
    <option value="NV">Nevada</option>
    <option value="OR">Oregon</option>
    <option value="WA">Washington</option>
  </optgroup>
</select>

.boldoption {
	font-weight: bold;
}

<select>
	<option>Some normal-font option</option>
	<option>Another normal-font option</option>
	<option class="boldoption">Some bold option</option>
</select>

option{
    font-size:18px;
    background-color:#ffffff;
}
option:before{
    content: ">";
    font-size:20px;
    display:none;
    padding-right:10px;
    padding-left:5px;
    color:#fff;
}
option:hover:before{
    display:inline;
}

function toggleSelect(){ 
 if (store.classList[0] === "hidden"){
    store.classList = "viewfull"
  }
  else {
    store.classList = "hidden"
  }
}

#store {
  overflow-y: scroll;
  max-height: 110px;
  max-width: 50%
 }
 
.hidden {
  display: none
 }
 
.viewfull {
  display: block
}

#store :nth-child(4) {
  background-color: lime;
}

span {font-size:2rem;cursor:pointer}

<span onclick="toggleSelect()">⮋</span>
 <div id="store" class="hidden">
 
<ul><li><a href="#keylogger">keylogger</a></li><li><a href="#1526269343113">1526269343113</a></li><li><a href="#slow">slow</a></li><li><a href="#slow2">slow2</a></li><li><a href="#Benchmark">Benchmark</a></li><li><a href="#modal">modal</a></li><li><a href="#buma">buma</a></li><li><a href="#1526099371108">1526099371108</a></li><a href="#1526099371108o">1526099371108o</a></li><li><a href="#pwnClrB">pwnClrB</a></li><li><a href="#stars%20u">stars%20u</a></li><li><a href="#pwnClrC">pwnClrC</a></li><li><a href="#stars ">stars </a></li><li><a href="#wello">wello</a></li><li><a href="#equalizer">equalizer</a></li><li><a href="#pwnClrA">pwnClrA</a></li></ul>
 
 </div>

	$(function() {
    var clicky;
    var t=0;
    $(document).mousedown(function(e) {
        clicky = $(e.target);
    });
    $(document).mouseup(function(e) {
        clicky = null;
    });

    $("select").focusout(function(e) {
        if (typeof clicky.attr('id') !== typeof undefined && clicky.attr('id') !== false) {
        	$(this).parents().children("span.selected").html(clicky.html());
        	$(this).children('option[value="'+clicky.attr('id')+'"]').prop('selected', true);
		}
        
        $(this).parents().children("span.lists").html('');
        

    });
    $('select > option').text(function(i, text) {
				var attr = $(this).attr('selected');
				if (typeof attr !== typeof undefined && attr !== false) {
        				$(this).parents().parents().children("span.selected").html(text);
				}
	});

		$("select").focusin(function(){
			$(this).children('option').text(function(i, text) {
    			$(this).parents().children("span.lists").append("<span class='item' id='"+$(this).attr('value')+"'>"+text+"</span>");
				});
		});

	});

select {
  width: 0px;
  height: 0px;
  overflow:hidden;
  outline: none;
  border: none;
  appearance:none;
  -moz-appearance: none;

}
label{
	display: inline-block;
	padding: 5px 10px;
	position: relative;
	width: 100px;
	height: 20px;
	background-color:#ccc;

}
label .selected{
	display: inline-block;
	overflow: hidden;
	width: 100%;
	height: 100%;
}
label span.lists{
	width: 100%;
	display: inline-block;
	position: absolute;
	top: 100%;
	left: 0px;
	box-shadow: 0px 0px 2px 0px #ccc;
	background-color:#fff;
	z-index: 9;
}
label span.item{
	display: inline-block;
	width: 100%;
	border-bottom: 1px solid #ccc;
}

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>
	<form action="?" method="GET">
	<label><span class="selected">select..</span> <span class="lists"></span>
	<select name="test">
		<option value="1">Lorem ipsum dolor sit amet, consectetur adipisicing elit.</option>
		<option value="2" selected>item 2</option>
		<option value="3">item 3</option>
		<option value="4">item 4</option>
	</select>
	</label><br>
	<label><span class="selected">select..</span> <span class="lists"></span>
	<select name="test2">
		<option value="1">Lorem ipsum dolor sit amet, consectetur adipisicing elit.</option>
		<option value="2">item 2</option>
		<option value="3" selected>item 3</option>
		<option value="4">item 4</option>
	</select>
	</label><br>
	<button>Submit</button>
</form>

</body>
</html>

var x, i, j, selElmnt, a, b, c;
/*look for any elements with the class "custom-select":*/
x = document.getElementsByClassName("custom-select");
for (i = 0; i < x.length; i++) {
  selElmnt = x[i].getElementsByTagName("select")[0];
  /*for each element, create a new DIV that will act as the selected item:*/
  a = document.createElement("DIV");
  a.setAttribute("class", "select-selected");
  a.innerHTML = selElmnt.options[selElmnt.selectedIndex].innerHTML;
  x[i].appendChild(a);
  /*for each element, create a new DIV that will contain the option list:*/
  b = document.createElement("DIV");
  b.setAttribute("class", "select-items select-hide");
  for (j = 1; j < selElmnt.length; j++) {
    /*for each option in the original select element,
    create a new DIV that will act as an option item:*/
    c = document.createElement("DIV");
    c.innerHTML = selElmnt.options[j].innerHTML;
    c.addEventListener("click", function(e) {
        /*when an item is clicked, update the original select box,
        and the selected item:*/
        var y, i, k, s, h;
        s = this.parentNode.parentNode.getElementsByTagName("select")[0];
        h = this.parentNode.previousSibling;
        for (i = 0; i < s.length; i++) {
          if (s.options[i].innerHTML == this.innerHTML) {
            s.selectedIndex = i;
            h.innerHTML = this.innerHTML;
            y = this.parentNode.getElementsByClassName("same-as-selected");
            for (k = 0; k < y.length; k++) {
              y[k].removeAttribute("class");
            }
            this.setAttribute("class", "same-as-selected");
            break;
          }
        }
        h.click();
    });
    b.appendChild(c);
  }
  x[i].appendChild(b);
  a.addEventListener("click", function(e) {
      /*when the select box is clicked, close any other select boxes,
      and open/close the current select box:*/
      e.stopPropagation();
      closeAllSelect(this);
      this.nextSibling.classList.toggle("select-hide");
      this.classList.toggle("select-arrow-active");
  });
}
function closeAllSelect(elmnt) {
  /*a function that will close all select boxes in the document,
  except the current select box:*/
  var x, y, i, arrNo = [];
  x = document.getElementsByClassName("select-items");
  y = document.getElementsByClassName("select-selected");
  for (i = 0; i < y.length; i++) {
    if (elmnt == y[i]) {
      arrNo.push(i)
    } else {
      y[i].classList.remove("select-arrow-active");
    }
  }
  for (i = 0; i < x.length; i++) {
    if (arrNo.indexOf(i)) {
      x[i].classList.add("select-hide");
    }
  }
}
/*if the user clicks anywhere outside the select box,
then close all select boxes:*/
document.addEventListener("click", closeAllSelect);

/*the container must be positioned relative:*/
.custom-select {
  position: relative;
  font-family: Arial;
}
.custom-select select {
  display: none; /*hide original SELECT element:*/
}
.select-selected {
  background-color: DodgerBlue;
}
/*style the arrow inside the select element:*/
.select-selected:after {
  position: absolute;
  content: "";
  top: 14px;
  right: 10px;
  width: 0;
  height: 0;
  border: 6px solid transparent;
  border-color: #fff transparent transparent transparent;
}
/*point the arrow upwards when the select box is open (active):*/
.select-selected.select-arrow-active:after {
  border-color: transparent transparent #fff transparent;
  top: 7px;
}
/*style the items (options), including the selected item:*/
.select-items div,.select-selected {
  color: #ffffff;
  padding: 8px 16px;
  border: 1px solid transparent;
  border-color: transparent transparent rgba(0, 0, 0, 0.1) transparent;
  cursor: pointer;
}
/*style items (options):*/
.select-items {
  position: absolute;
  background-color: DodgerBlue;
  top: 100%;
  left: 0;
  right: 0;
  z-index: 99;
}
/*hide the items when the select box is closed:*/
.select-hide {
  display: none;
}
.select-items div:hover, .same-as-selected {
  background-color: rgba(0, 0, 0, 0.1);
}

<div class="custom-select" style="width:200px;">
  <select>
    <option value="0">Select car:</option>
    <option value="1">Audi</option>
    <option value="2">BMW</option>
    <option value="3">Citroen</option>
    <option value="4">Ford</option>
    <option value="5">Honda</option>
    <option value="6">Jaguar</option>
    <option value="7">Land Rover</option>
    <option value="8">Mercedes</option>
    <option value="9">Mini</option>
    <option value="10">Nissan</option>
    <option value="11">Toyota</option>
    <option value="12">Volvo</option>
  </select>
</div>