(function( $ ) {
    $.widget( "custom.combobox", {
      _create: function() {
        this.wrapper = $( "<span>" )
          .addClass( "custom-combobox" )
          .insertAfter( this.element );
 
        this.element.hide();
        this._createAutocomplete();
        this._createShowAllButton();
      },
 
      _createAutocomplete: function() {
        var selected = this.element.children( ":selected" ),
          value = selected.val() ? selected.text() : "";
 
        this.input = $( "<input>" )
          .appendTo( this.wrapper )
          .val( value )
          .attr( "title", "" )
          .addClass( "custom-combobox-input ui-widget ui-widget-content ui-state-default ui-corner-left" )
          .autocomplete({
            delay: 0,
            minLength: 0,
			
 open: function() { $('ul.ui-autocomplete').width($( "input.custom-combobox-input" ).width() + 20 + "px") } ,
            source: $.proxy( this, "_source" )
          })
        
 
        this._on( this.input, {
          autocompleteselect: function( event, ui ) {
            ui.item.option.selected = true;
            this._trigger( "select", event, {
              item: ui.item.option
            });
          },
 
          autocompletechange: "_removeIfInvalid"
        });
      },
 
      _createShowAllButton: function() {
        var input = this.input,
          wasOpen = false;
 
        $( "<a>" )
          .attr( "tabIndex", -1 )
                .appendTo( this.wrapper )
          .button({
            icons: {
              primary: "ui-icon-triangle-1-s"
            },
            text: false
          })
          .removeClass( "ui-corner-all" )
          .addClass( "custom-combobox-toggle ui-corner-right" )
          .mousedown(function() {
            wasOpen = input.autocomplete( "widget" ).is( ":visible" );
          })
          .click(function() {
            input.focus();
 
            // Close if already visible
            if ( wasOpen ) {
              return;
            }
 
            // Pass empty string as value to search for, displaying all results
            input.autocomplete( "search", "" );
          });
      },
 
      _source: function( request, response ) {
        var matcher = new RegExp( $.ui.autocomplete.escapeRegex(request.term), "i" );
        response( this.element.children( "option" ).map(function() {
          var text = $( this ).text();
          if ( this.value && ( !request.term || matcher.test(text) ) )
            return {
              label: text,
              value: text,
              option: this
            };
        }) );
      },
 
      _removeIfInvalid: function( event, ui ) {
 
        // Selected an item, nothing to do
        if ( ui.item ) {
          return;
        }
 
        // Search for a match (case-insensitive)
        var value = this.input.val(),
          valueLowerCase = value.toLowerCase(),
          valid = false;
        this.element.children( "option" ).each(function() {
          if ( $( this ).text().toLowerCase() === valueLowerCase ) {
            this.selected = valid = true;
            return false;
          }
        });
 
        // Found a match, nothing to do
        if ( valid ) {
          return;
        }
 
        // Remove invalid value
        this.input
          .val( "" )
                this.element.val( "" );
     
        this.input.autocomplete( "instance" ).term = "";
      },
 
      _destroy: function() {
        this.wrapper.remove();
        this.element.show();
      }
	  
	     
	  
	  
	  
	  
    });
	
	
	
  })( jQuery );
  
  
  
  $(document).ready(function(){
    
    
    $("#combobox").combobox();
    
	     $.ui.autocomplete.prototype._renderItem = function (ul, item) {
            item.label = item.label.replace(new RegExp("(?![^&;]+;)(?!<[^<>]*)(" + $.ui.autocomplete.escapeRegex(this.term) + ")(?![^<>]*>)(?![^&;]+;)", "gi"), "<strong>$1</strong>");
            return $("<li></li>")
                    .data("item.autocomplete", item)
                    .append("<a>" + item.label + "</a>")
                    .appendTo(ul);
        };
	  
	  
	  
	  
	  
	  
	  

       });
  
  
  
  
 

  .custom-combobox {
    position: relative;
    display: inline-block;
	width:100%;
  }
  .custom-combobox-toggle {
    position: absolute;
    top: 0;
    bottom: 0;
    margin-left: -1px;
    padding: 0;
width: 20px;

	
  }
  ul.ui-autocomplete{
  max-height:200px;
  overflow:auto;
  	
  
  }
.ui-autocomplete-term { font-weight: bold; color: blue; }
  .ui-state-focus{
  background:none !important;
    background-color: blue !important;
	border:none !important;
}
  
  .custom-combobox-input {
 
  background-color:green !important;
    margin: 0;
  
background:initial;
  }

<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script src="http://code.jquery.com/ui/1.10.2/jquery-ui.js"></script>
<script type="text/javascript" src="jquery.ui.combobox.js"></script>
<link rel="stylesheet" href="http://code.jquery.com/ui/1.10.2/themes/smoothness/jquery-ui.css" />


<div style="background-color:red;width:70%">
  <select id="combobox">
    <option value="">Select one...</option>
    <option value="ActionScript">ActionScript</option>
    <option value="AppleScript">AppleScript</option>
  
  </select>
<div/>