What you ask is impossible! Because select element is rendered by the OS and not HTML. It cannot be styled via CSS. So you have to think alternative .I thought to create a dropdown from <ul> list and <li> options.So I created this one bellow: http://jsfiddle.net/csdtesting/ks09u3kd/ .And now YES you have can whatever option you want in whatever style!

DROPDOWN WITH UL AND LI AS HTML SELECT ELEMENT

(function($, undefined) {
  var open = [];

  var opts = {
    selector: '.dropdown',
    toggle: 'dropdown-toggle',
    open: 'dropdown-open',
    nest: true
  };

  $(document).on('click.dropdown touchstart.dropdown', function(e) {
    // Close the last open dropdown if click is from outside the target dropdown
    if (open.length && (!opts.nest || !open[open.length - 1].find(e.target).length)) {
      open.pop().removeClass(opts.open);
    }

    var $this = $(e.target);

    // If target is a dropdown then toggle it...
    if ($this.hasClass(opts.toggle)) {
      e.preventDefault();

      $this = $this.closest(opts.selector);

      if (!$this.hasClass(opts.open)) {
        open.push($this.addClass(opts.open));
      } else {
        open.pop().removeClass(opts.open);
      }
    }
  });

})(jQuery);

.dropdown {
  float: left;
  position: relative;
  width: 200px;
  padding: 5px;
  margin-right: 10px;
  background: #ccc;
}
.dropdown a {
  display: block;
  text-decoration: none;
  color: #333;
}
ul.dropdown-menu li:nth-child(2) {
  font-weight: bold;
}
/* toggle */

.dropdown .dropdown-toggle {
  padding: 0;
}
/* dropdown */

.dropdown-menu {
  position: absolute;
  top: 100%;
  right: 0;
  left: 0;
  display: none;
  margin: 0;
  padding: 0;
  list-style-type: none;
  background: #ccc;
}
/* options */

.dropdown-menu .option a {
  padding: 5px;
}
.dropdown-menu .option a:hover {
  background-color: #aaa;
}
/* open */

.dropdown-open {
  z-index: 400;
}
.dropdown-open > .dropdown-menu {
  display: block;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="divSelect" class="dropdown">
  <a href="#options" class="dropdown-toggle">Manni </a>
  <ul class="dropdown-menu">
    <li class="option"><a href="#">Manni - Haraldarmanni</a>
    </li>
    <li class="option"><a href="#">Manni - Hornafjarðarmanni</a>
    </li>
    <li class="option"><a href="#">Manni - Laugarvatnsmanni</a>
    </li>
    <li class="option"><a href="#">Manni - Trjámann</a>
    </li>
  </ul>
</div>

If we were to code what you ask in pure JS: FIDDLE

<div id="fakeSelect">
    <div id="selectBox"></div>
    <ul id="selectOptionsBox">
        <li>Manni</li>
        <li>Manni - Haraldarmanni</li>
        <li>Manni - <b>Hornafjarðarmanni</b></li>
        <li>Manni - Laugarvatnsmanni</li>
        <li>Marglita hálfmáninn</li>
        <li>Marglita klukkan</li>
        <li>Marías</li>
        <li>Mausel</li>
        <li>Málverkasafnið</li>
        <li>Mexíkanskur veltipóker</li>
        <li>Miklar hindranir</li>
        <li>Monte Carlo</li>
    </ul>
</div>

#fakeSelect {
    user-select: none;
    -webkit-user-select: none;
}
#selectBox {
    width: calc(200px - 4px);
    border: 1px solid silver;
    padding: 2px;
    cursor: default;
    font: 13px Arial, sans-serif;
    position: relative;
}
#selectBox:hover {
    border: 1px solid gray;
}
#selectBox::after {
    position: absolute;
    content: "▼";
    font-size: .8em;
    right: 5px;
    top: 5px;
}
#selectOptionsBox {
    list-style: none;
    margin: 0;
    padding: 0;
    width: 200px;
    border: 1px solid silver;
    border-top: none;
    overflow: auto;
    height: 150px;
    cursor: default;
    font: 13px Arial, sans-serif;
    display: none;
}
#selectOptionsBox li {
    padding: 2px;
}
#selectOptionsBox li:hover {
    background: gainsboro;
}

var selectBox = document.getElementById("selectBox");
var selectOptionsBox = document.getElementById("selectOptionsBox");
var selectOptions = selectOptionsBox.getElementsByTagName("li");

selectBox.innerHTML = selectOptions[0].innerHTML;

selectBox.onclick = function() {
    if (selectOptionsBox.style.display != "block") {
        selectOptionsBox.style.display = "block";
    } else {
        selectOptionsBox.style.display = "none";
    }
}
window.onclick = function(e) {
    if (e.target != selectBox &&
        selectOptionsBox.style.display == "block") {
        selectOptionsBox.style.display = "none";
    }
}

for (var i = 0; i < selectOptions.length; i++) {
    (function(i) {
        selectOptions[i].onclick = function() {
            selectBox.innerHTML = this.innerHTML;
        }
    })(i);
}