diff --git a/.npmignore b/.npmignore
index 9b079aa..0a13a28 100644
--- a/.npmignore
+++ b/.npmignore
@@ -1,6 +1,5 @@
 demo
 dist
-node_modules
 src
 .gitignore
 .jshintrc
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 93c30a9..c9fd157 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+## 0.3.1 - 2015-01-13
+
+Added: new `buttonActive` property for the `classNames` prop - this will be
+used when one or more options are selected, otherwise `button` will be used.
+
+Changed: `classNames` prop no longer has to provide all properties - defaults
+will be used where not provided.
+
 ## 0.3.0 - 2015-01-01
 
 Added: double-clicking now adds the selected option to the selection.
diff --git a/README.md b/README.md
index 7ff1885..7bcb120 100644
--- a/README.md
+++ b/README.md
@@ -95,7 +95,9 @@ objects each time the selection is added to.
 
 `className` - class name for the component's `<div>` container.
 
-`classNames` - class names for each of the component's child elements.
+`classNames` - class names for each of the component's child elements. See the
+default props below for properties. Defaults will be used for any properties not
+specified via this prop.
 
 `defaultFilter` - default filter text to be applied to the `<select>`
 
@@ -122,6 +124,8 @@ the `value` for its `<option>`.
   className: 'FilteredMultiSelect',
   classNames: {
     button: 'FilteredMultiSelect__button',
+    // Used when at least one <option> is selected
+    buttonActive: 'FilteredMultiSelect__button--active',
     filter: 'FilteredMultiSelect__filter',
     select: 'FilteredMultiSelect__select'
   }
diff --git a/demo/app.jsx b/demo/app.jsx
index 127a520..a9f4b1a 100644
--- a/demo/app.jsx
+++ b/demo/app.jsx
@@ -257,6 +257,7 @@ var bootstrapClasses = {
   filter: 'form-control'
 , select: 'form-control'
 , button: 'btn btn btn-block btn-default'
+, buttonActive: 'btn btn btn-block btn-primary'
 }
 
 var BasicSelection = React.createClass({
@@ -352,7 +353,12 @@ var AddRemoveSelection = React.createClass({
       <div className="col-md-5">
         <FilteredMultiSelect
           buttonText="Remove"
-          classNames={bootstrapClasses}
+          classNames={{
+            filter: 'form-control'
+          , select: 'form-control'
+          , button: 'btn btn btn-block btn-default'
+          , buttonActive: 'btn btn btn-block btn-danger'
+          }}
           onChange={this._onDeselect}
           options={selectedOptions}
           textProp="name"
diff --git a/dist/react-filtered-multiselect.js b/dist/react-filtered-multiselect.js
index 6fd7189..5da6577 100644
--- a/dist/react-filtered-multiselect.js
+++ b/dist/react-filtered-multiselect.js
@@ -1,5 +1,5 @@
-/**
- * react-filtered-multiselect 0.3.0 - https://github.com/insin/react-filtered-multiselect
+/*!
+ * react-filtered-multiselect 0.3.1 - https://github.com/insin/react-filtered-multiselect
  * MIT Licensed
  */
 !function(e){if("object"==typeof exports&&"undefined"!=typeof module)module.exports=e();else if("function"==typeof define&&define.amd)define([],e);else{var f;"undefined"!=typeof window?f=window:"undefined"!=typeof global?f=global:"undefined"!=typeof self&&(f=self),f.FilteredMultiSelect=e()}}(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){
@@ -35,6 +35,13 @@ function getItemsByProp(arr, prop, values) {
   return items
 }
 
+var DEFAULT_CLASS_NAMES = {
+  button: 'FilteredMultiSelect__button'
+, buttonActive: 'FilteredMultiSelect__button--active'
+, filter: 'FilteredMultiSelect__filter'
+, select: 'FilteredMultiSelect__select'
+}
+
 var FilteredMultiSelect = React.createClass({displayName: 'FilteredMultiSelect',
   propTypes: {
     buttonText: React.PropTypes.string
@@ -55,11 +62,7 @@ var FilteredMultiSelect = React.createClass({displayName: 'FilteredMultiSelect',
     return {
       buttonText: 'Select'
     , className: 'FilteredMultiSelect'
-    , classNames: {
-        button: 'FilteredMultiSelect__button'
-      , filter: 'FilteredMultiSelect__filter'
-      , select: 'FilteredMultiSelect__select'
-      }
+    , classNames: {}
     , defaultFilter: ''
     , disabled: false
     , placeholder: 'type to filter'
@@ -98,6 +101,19 @@ var FilteredMultiSelect = React.createClass({displayName: 'FilteredMultiSelect',
     }
   },
 
+  _getClassName:function(name) {
+    if (arguments.length == 1) {
+      return this.props.classNames[name] || DEFAULT_CLASS_NAMES[name]
+    }
+
+    for (var i = 0, l = arguments.length; i < l ; i++) {
+      if (arguments[i] in this.props.classNames) {
+        return this.props.classNames[arguments[i]]
+      }
+    }
+    return DEFAULT_CLASS_NAMES[name]
+  },
+
   _filterOptions:function(filter, selectedOptions, options) {
     if (typeof filter == 'undefined') {
       filter = this.state.filter
@@ -176,10 +192,11 @@ var FilteredMultiSelect = React.createClass({displayName: 'FilteredMultiSelect',
 
   render:function() {
     var $__0=   this,props=$__0.props,state=$__0.state
+    var hasSelectedOptions = state.selectedValues.length > 0
     return React.createElement("div", {className: props.className}, 
       React.createElement("input", {
          type: "text", 
-         className: props.classNames.filter, 
+         className: this._getClassName('filter'), 
          placeholder: props.placeholder, 
          value: state.filter, 
          onChange: this._onFilterChange, 
@@ -188,7 +205,7 @@ var FilteredMultiSelect = React.createClass({displayName: 'FilteredMultiSelect',
       ), 
       React.createElement("select", {multiple: true, 
          ref: "select", 
-         className: props.classNames.select, 
+         className: this._getClassName('select'), 
          size: props.size, 
          value: state.selectedValues, 
          onChange: this._updateSelectedValues, 
@@ -199,8 +216,8 @@ var FilteredMultiSelect = React.createClass({displayName: 'FilteredMultiSelect',
         })
       ), 
       React.createElement("button", {type: "button", 
-         className: props.classNames.button, 
-         disabled: state.selectedValues.length === 0, 
+         className: hasSelectedOptions ? this._getClassName('buttonActive', 'button') : this._getClassName('button'), 
+         disabled: !hasSelectedOptions, 
          onClick: this._addSelectedToSelection}, 
         this.props.buttonText
       )
diff --git a/dist/react-filtered-multiselect.min.js b/dist/react-filtered-multiselect.min.js
index 5a75b7e..c04d0ac 100644
--- a/dist/react-filtered-multiselect.min.js
+++ b/dist/react-filtered-multiselect.min.js
@@ -1,5 +1,5 @@
-/**
- * react-filtered-multiselect 0.3.0 - https://github.com/insin/react-filtered-multiselect
+/*!
+ * react-filtered-multiselect 0.3.1 - https://github.com/insin/react-filtered-multiselect
  * MIT Licensed
  */
-!function(e){if("object"==typeof exports&&"undefined"!=typeof module)module.exports=e();else if("function"==typeof define&&define.amd)define([],e);else{var t;"undefined"!=typeof window?t=window:"undefined"!=typeof global?t=global:"undefined"!=typeof self&&(t=self),t.FilteredMultiSelect=e()}}(function(){return function e(t,s,i){function n(l,r){if(!s[l]){if(!t[l]){var p="function"==typeof require&&require;if(!r&&p)return p(l,!0);if(o)return o(l,!0);var a=new Error("Cannot find module '"+l+"'");throw a.code="MODULE_NOT_FOUND",a}var d=s[l]={exports:{}};t[l][0].call(d.exports,function(e){var s=t[l][1][e];return n(s?s:e)},d,d.exports,e,t,s,i)}return s[l].exports}for(var o="function"==typeof require&&require,l=0;l<i.length;l++)n(i[l]);return n}({1:[function(e,t){"use strict";function s(e,t){for(var s={},i=0,n=e.length;n>i;i++)t?s[e[i][t]]=!0:s[e[i]]=!0;return s}function i(e,t,i){for(var n=[],o=0,l=s(i),r=0,p=e.length,a=i.length;p>r&&a>o;r++)l[e[r][t]]&&(n.push(e[r]),o++);return n}var n="undefined"!=typeof window?window.React:"undefined"!=typeof global?global.React:null,o=n.createClass({displayName:"FilteredMultiSelect",propTypes:{buttonText:n.PropTypes.string,className:n.PropTypes.string,classNames:n.PropTypes.object,defaultFilter:n.PropTypes.string,disabled:n.PropTypes.bool,onChange:n.PropTypes.func.isRequired,options:n.PropTypes.array.isRequired,placeholder:n.PropTypes.string,selectedOptions:n.PropTypes.array,size:n.PropTypes.number,textProp:n.PropTypes.string,valueProp:n.PropTypes.string},getDefaultProps:function(){return{buttonText:"Select",className:"FilteredMultiSelect",classNames:{button:"FilteredMultiSelect__button",filter:"FilteredMultiSelect__filter",select:"FilteredMultiSelect__select"},defaultFilter:"",disabled:!1,placeholder:"type to filter",size:6,selectedOptions:[],textProp:"text",valueProp:"value"}},getInitialState:function(){var e=this.props,t=e.defaultFilter,s=e.selectedOptions;return{filter:t,filteredOptions:this._filterOptions(t,s),selectedValues:[]}},componentWillReceiveProps:function(e){(e.options!==this.props.options||e.selectedOptions!==this.props.selectedOptions||e.options.length!=this.props.options.length||e.selectedOptions.length!=this.props.selectedOptions.length)&&this.setState({filteredOptions:this._filterOptions(this.state.filter,e.selectedOptions,e.options)},this._updateSelectedValues)},_filterOptions:function(e,t,i){"undefined"==typeof e&&(e=this.state.filter),"undefined"==typeof t&&(t=this.props.selectedOptions),"undefined"==typeof i&&(i=this.props.options),e=e.toUpperCase();for(var n=this.props,o=n.textProp,l=n.valueProp,r=s(t,l),p=[],a=0,d=i.length;d>a;a++)r[i[a][l]]||e&&-1==i[a][o].toUpperCase().indexOf(e)||p.push(i[a]);return p},_onFilterChange:function(e){var t=e.target.value;this.setState({filter:t,filteredOptions:this._filterOptions(t)},this._updateSelectedValues)},_onFilterKeyPress:function(e){if("Enter"==e.key&&(e.preventDefault(),1==this.state.filteredOptions.length)){var t=this.state.filteredOptions[0],s=this.props.selectedOptions.concat([t]);this.setState({filter:"",selectedValues:[]},function(){this.props.onChange(s)}.bind(this))}},_updateSelectedValues:function(e){for(var t=e?e.target:this.refs.select.getDOMNode(),s=[],i=0,n=t.options.length;n>i;i++)t.options[i].selected&&s.push(t.options[i].value);(e||String(this.state.selectedValues)!=String(s))&&this.setState({selectedValues:s})},_addSelectedToSelection:function(){var e=this.props.selectedOptions.concat(i(this.state.filteredOptions,this.props.valueProp,this.state.selectedValues));this.setState({selectedValues:[]},function(){this.props.onChange(e)}.bind(this))},render:function(){var e=this,t=e.props,s=e.state;return n.createElement("div",{className:t.className},n.createElement("input",{type:"text",className:t.classNames.filter,placeholder:t.placeholder,value:s.filter,onChange:this._onFilterChange,onKeyPress:this._onFilterKeyPress,disabled:t.disabled}),n.createElement("select",{multiple:!0,ref:"select",className:t.classNames.select,size:t.size,value:s.selectedValues,onChange:this._updateSelectedValues,onDoubleClick:this._addSelectedToSelection,disabled:t.disabled},this.state.filteredOptions.map(function(e){return n.createElement("option",{key:e[t.valueProp],value:e[t.valueProp]},e[t.textProp])})),n.createElement("button",{type:"button",className:t.classNames.button,disabled:0===s.selectedValues.length,onClick:this._addSelectedToSelection},this.props.buttonText))}});t.exports=o},{}]},{},[1])(1)});
\ No newline at end of file
+!function(e){if("object"==typeof exports&&"undefined"!=typeof module)module.exports=e();else if("function"==typeof define&&define.amd)define([],e);else{var t;"undefined"!=typeof window?t=window:"undefined"!=typeof global?t=global:"undefined"!=typeof self&&(t=self),t.FilteredMultiSelect=e()}}(function(){return function e(t,s,i){function n(l,r){if(!s[l]){if(!t[l]){var a="function"==typeof require&&require;if(!r&&a)return a(l,!0);if(o)return o(l,!0);var p=new Error("Cannot find module '"+l+"'");throw p.code="MODULE_NOT_FOUND",p}var u=s[l]={exports:{}};t[l][0].call(u.exports,function(e){var s=t[l][1][e];return n(s?s:e)},u,u.exports,e,t,s,i)}return s[l].exports}for(var o="function"==typeof require&&require,l=0;l<i.length;l++)n(i[l]);return n}({1:[function(e,t){"use strict";function s(e,t){for(var s={},i=0,n=e.length;n>i;i++)t?s[e[i][t]]=!0:s[e[i]]=!0;return s}function i(e,t,i){for(var n=[],o=0,l=s(i),r=0,a=e.length,p=i.length;a>r&&p>o;r++)l[e[r][t]]&&(n.push(e[r]),o++);return n}var n="undefined"!=typeof window?window.React:"undefined"!=typeof global?global.React:null,o={button:"FilteredMultiSelect__button",buttonActive:"FilteredMultiSelect__button--active",filter:"FilteredMultiSelect__filter",select:"FilteredMultiSelect__select"},l=n.createClass({displayName:"FilteredMultiSelect",propTypes:{buttonText:n.PropTypes.string,className:n.PropTypes.string,classNames:n.PropTypes.object,defaultFilter:n.PropTypes.string,disabled:n.PropTypes.bool,onChange:n.PropTypes.func.isRequired,options:n.PropTypes.array.isRequired,placeholder:n.PropTypes.string,selectedOptions:n.PropTypes.array,size:n.PropTypes.number,textProp:n.PropTypes.string,valueProp:n.PropTypes.string},getDefaultProps:function(){return{buttonText:"Select",className:"FilteredMultiSelect",classNames:{},defaultFilter:"",disabled:!1,placeholder:"type to filter",size:6,selectedOptions:[],textProp:"text",valueProp:"value"}},getInitialState:function(){var e=this.props,t=e.defaultFilter,s=e.selectedOptions;return{filter:t,filteredOptions:this._filterOptions(t,s),selectedValues:[]}},componentWillReceiveProps:function(e){(e.options!==this.props.options||e.selectedOptions!==this.props.selectedOptions||e.options.length!=this.props.options.length||e.selectedOptions.length!=this.props.selectedOptions.length)&&this.setState({filteredOptions:this._filterOptions(this.state.filter,e.selectedOptions,e.options)},this._updateSelectedValues)},_getClassName:function(e){if(1==arguments.length)return this.props.classNames[e]||o[e];for(var t=0,s=arguments.length;s>t;t++)if(arguments[t]in this.props.classNames)return this.props.classNames[arguments[t]];return o[e]},_filterOptions:function(e,t,i){"undefined"==typeof e&&(e=this.state.filter),"undefined"==typeof t&&(t=this.props.selectedOptions),"undefined"==typeof i&&(i=this.props.options),e=e.toUpperCase();for(var n=this.props,o=n.textProp,l=n.valueProp,r=s(t,l),a=[],p=0,u=i.length;u>p;p++)r[i[p][l]]||e&&-1==i[p][o].toUpperCase().indexOf(e)||a.push(i[p]);return a},_onFilterChange:function(e){var t=e.target.value;this.setState({filter:t,filteredOptions:this._filterOptions(t)},this._updateSelectedValues)},_onFilterKeyPress:function(e){if("Enter"==e.key&&(e.preventDefault(),1==this.state.filteredOptions.length)){var t=this.state.filteredOptions[0],s=this.props.selectedOptions.concat([t]);this.setState({filter:"",selectedValues:[]},function(){this.props.onChange(s)}.bind(this))}},_updateSelectedValues:function(e){for(var t=e?e.target:this.refs.select.getDOMNode(),s=[],i=0,n=t.options.length;n>i;i++)t.options[i].selected&&s.push(t.options[i].value);(e||String(this.state.selectedValues)!=String(s))&&this.setState({selectedValues:s})},_addSelectedToSelection:function(){var e=this.props.selectedOptions.concat(i(this.state.filteredOptions,this.props.valueProp,this.state.selectedValues));this.setState({selectedValues:[]},function(){this.props.onChange(e)}.bind(this))},render:function(){var e=this,t=e.props,s=e.state,i=s.selectedValues.length>0;return n.createElement("div",{className:t.className},n.createElement("input",{type:"text",className:this._getClassName("filter"),placeholder:t.placeholder,value:s.filter,onChange:this._onFilterChange,onKeyPress:this._onFilterKeyPress,disabled:t.disabled}),n.createElement("select",{multiple:!0,ref:"select",className:this._getClassName("select"),size:t.size,value:s.selectedValues,onChange:this._updateSelectedValues,onDoubleClick:this._addSelectedToSelection,disabled:t.disabled},this.state.filteredOptions.map(function(e){return n.createElement("option",{key:e[t.valueProp],value:e[t.valueProp]},e[t.textProp])})),n.createElement("button",{type:"button",className:i?this._getClassName("buttonActive","button"):this._getClassName("button"),disabled:!i,onClick:this._addSelectedToSelection},this.props.buttonText))}});t.exports=l},{}]},{},[1])(1)});
\ No newline at end of file
diff --git a/package.json b/package.json
index a8d7174..f8a7b2d 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "react-filtered-multiselect",
   "description": "Filtered multi-select React component",
-  "version": "0.3.0",
+  "version": "0.3.1",
   "main": "./lib/index.js",
   "homepage": "https://github.com/insin/react-filtered-multiselect",
   "standalone": "FilteredMultiSelect",
diff --git a/src/index.jsx b/src/index.jsx
index f6f4130..35fd839 100644
--- a/src/index.jsx
+++ b/src/index.jsx
@@ -30,6 +30,13 @@ function getItemsByProp(arr, prop, values) {
   return items
 }
 
+var DEFAULT_CLASS_NAMES = {
+  button: 'FilteredMultiSelect__button'
+, buttonActive: 'FilteredMultiSelect__button--active'
+, filter: 'FilteredMultiSelect__filter'
+, select: 'FilteredMultiSelect__select'
+}
+
 var FilteredMultiSelect = React.createClass({
   propTypes: {
     buttonText: React.PropTypes.string
@@ -50,11 +57,7 @@ var FilteredMultiSelect = React.createClass({
     return {
       buttonText: 'Select'
     , className: 'FilteredMultiSelect'
-    , classNames: {
-        button: 'FilteredMultiSelect__button'
-      , filter: 'FilteredMultiSelect__filter'
-      , select: 'FilteredMultiSelect__select'
-      }
+    , classNames: {}
     , defaultFilter: ''
     , disabled: false
     , placeholder: 'type to filter'
@@ -93,6 +96,19 @@ var FilteredMultiSelect = React.createClass({
     }
   },
 
+  _getClassName(name) {
+    if (arguments.length == 1) {
+      return this.props.classNames[name] || DEFAULT_CLASS_NAMES[name]
+    }
+
+    for (var i = 0, l = arguments.length; i < l ; i++) {
+      if (arguments[i] in this.props.classNames) {
+        return this.props.classNames[arguments[i]]
+      }
+    }
+    return DEFAULT_CLASS_NAMES[name]
+  },
+
   _filterOptions(filter, selectedOptions, options) {
     if (typeof filter == 'undefined') {
       filter = this.state.filter
@@ -171,10 +187,11 @@ var FilteredMultiSelect = React.createClass({
 
   render() {
     var {props, state} = this
+    var hasSelectedOptions = state.selectedValues.length > 0
     return <div className={props.className}>
       <input
          type="text"
-         className={props.classNames.filter}
+         className={this._getClassName('filter')}
          placeholder={props.placeholder}
          value={state.filter}
          onChange={this._onFilterChange}
@@ -183,7 +200,7 @@ var FilteredMultiSelect = React.createClass({
       />
       <select multiple
          ref="select"
-         className={props.classNames.select}
+         className={this._getClassName('select')}
          size={props.size}
          value={state.selectedValues}
          onChange={this._updateSelectedValues}
@@ -194,8 +211,8 @@ var FilteredMultiSelect = React.createClass({
         })}
       </select>
       <button type="button"
-         className={props.classNames.button}
-         disabled={state.selectedValues.length === 0}
+         className={hasSelectedOptions ? this._getClassName('buttonActive', 'button') : this._getClassName('button')}
+         disabled={!hasSelectedOptions}
          onClick={this._addSelectedToSelection}>
         {this.props.buttonText}
       </button>