A Pen by A Non Ymous.

index.html

<!-- Header
—————————————————————————————————————————-->
<h1>Hey World</h1>
<p class="head-text">This is a collection of Flat UI elements.</p>

<!-- CSS Menus
—————————————————————————————————————————-->
<p>
<nav class="blue">
  <li><a href="#">Joey</a></li>
  <li><a href="#">Profile</a></li>
  <li><a href="#">Work</a></li>
  <li><a href="#">Blog</a></li>
  <li><a href="#">Contact</a></li>
  <input class="nav-search" type="text" placeholder="Search..."/>
</nav>

<nav class="turq">
  <li><a href="#">Joey</a></li>
  <li><a href="#">Profile</a></li>
  <li><a href="#">Work</a></li>
  <li><a href="#">Blog</a></li>
  <li><a href="#">Contact</a></li>
  <input class="nav-search" type="text" placeholder="Search..."/>
</nav>

<nav class="dark">
  <li><a href="#">Joey</a></li>
  <li><a href="#">Profile</a></li>
  <li><a href="#">Work</a></li>
  <li><a href="#">Blog</a></li>
  <li><a href="#">Contact</a></li>
  <input class="nav-search" type="text" placeholder="Search..."/>
</nav>

<nav class="sun">
  <li><a href="#">Joey</a></li>
  <li><a href="#">Profile</a></li>
  <li><a href="#">Work</a></li>
  <li><a href="#">Blog</a></li>
  <li><a href="#">Contact</a></li>
  <input class="nav-search" type="text" placeholder="Search..."/>
</nav>

<nav class="red">
  <li><a href="#">Joey</a></li>
  <li><a href="#">Profile</a></li>
  <li><a href="#">Work</a></li>
  <li><a href="#">Blog</a></li>
  <li><a href="#">Contact</a></li>
  <input class="nav-search" type="text" placeholder="Search..."/>
</nav>
</p>

<!-- Checkbox Normal
—————————————————————————————————————————-->
<p>
  <input class="check turq" type="checkbox"/>
  <input class="check blue" type="checkbox"/>
  <input class="check yellow" type="checkbox"/>
  <input class="check red" type="checkbox"/>
  <input class="check dark" type="checkbox"/>
  <input class="check sun" type="checkbox"/>
</p>

<!-- Checkbox Circles
—————————————————————————————————————————-->
<p>
  <input class="circles sun" type="checkbox"/>
  <input class="circles dark" type="checkbox"/>
  <input class="circles blue" type="checkbox"/>
  <input class="circles turq" type="checkbox"/>
  <input class="circles yellow" type="checkbox"/>
  <input class="circles red" type="checkbox"/>
</p>

<!-- Radio Buttons
—————————————————————————————————————————-->
<p>
  <input checked class="radio blue" type="radio" name="null" value="hello"/>
  <input class="radio red" type="radio" name="null" value="hi"/>
  <input class="radio turq" type="radio" name="null" value="hola"/>
  <input class="radio sun" type="radio" name="null" value="yo"/>
</p>

<!-- Search, yo
—————————————————————————————————————————-->
<p>
  <input class="search sun" type="text" placeholder="Search"/>
  <input class="search turq" type="text" placeholder="Search"/>
  <input class="search blue" type="text" placeholder="Search"/>
  <input class="search red" type="text" placeholder="Search"/>
</p>

<!-- Dropdown Menu
—————————————————————————————————————————-->
<p>
  <div class="drop-wrap">
    <div class="main-drop">
      Menu
      <span>
        <img src="http://static.tumblr.com/upanoab/WRTmmcfvs/drop-down.png"/>
      </span>
    </div>
    <ul>
      <li>Waddup</li>
      <li>Color</li>
      <li>Links</li>
      <li>Yolo</li>
    </ul>
  </div>
</p>

<!-- Range
—————————————————————————————————————————-->
<p>
  <input type="range" min="0" max="50" value="0" step="0"/>
</p>

script.js

$(document).ready(function(e){
   $('.drop-wrap').on('click',function(){
      $('.drop-wrap ul').slideToggle();
   });
})

//Make sure you scroll down

style.css

*,
*:after,
*:before {
    box-sizing: border-box;
    font-family:'Open Sans';
    outline:0;
    text-shadow: 0 1px 1px rgba(255,255,255,0.3);
    -webkit-font-smoothing: antialiased;
}

body {
  text-align:center;
  margin-top:50px;
  margin-bottom:200px;
}


/* Header 
===============================*/

.head-text {
  width:300px;
  margin:-10px auto;
  margin-bottom:40px;
  line-height:1.4em;
  color:#777;
}

/* Main Colors
===============================*/
.turq {background:#16A085;}
.turq:checked {background:#1ABC9C;}

.blue {background:#2980B9;}
.blue:checked {background:#3498DB;}

.yellow {background:#eeca5a;}
.yellow:checked {background:#ffdc70;}

.red {background:#C0392B;}
.red:checked {background:#E74C3C;}

.dark {background:#2C3E50;}
.dark:checked {background:#34495E;}

.sun {background:#F39C12;}
.sun:checked {background:#F1C40F;}

/* CSS Menus
===============================*/
nav {
  position:relative;
  width:700px;
  margin:30px auto;
  margin-bottom:40px;
  -webkit-border-radius:6px;
     -moz-border-radius:6px;
          border-radius:6px;
  padding:15px;
  text-align:left;
}

li {
  list-style:none;
  color:#fff;
  font-weight:600;
  display:inline-block;
}

li > a, a:visited {
  padding:15px;
  color:#fff;
  text-decoration:none;
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

li > a:hover {
  background:rgba(0, 0, 0, 0.1);
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

.nav-search {
  position:absolute;
  right:9px;
  top:13px;
  background:rgba(0, 0, 0, 0.1);
  -webkit-border-radius:6px;
     -moz-border-radius:6px;
          border-radius:6px;
  border:none;
  padding:5px;
  padding-left:15px;
  outline:none;
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

.nav-search:focus {
  background:#fff;
  font-weight:600;
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

.nav-search::-webkit-input-placeholder {
   color: #FFF;
}

.nav-search:-moz-placeholder { 
   color: #FFF;
}

.nav-search::-moz-placeholder {
   color: #FFF;
}

.nav-search:-ms-input-placeholder {  
   color: #FFF;
}


/* Default Checkbox
===============================*/
.check {
  position:relative;
  -webkit-appearance: none;
  -moz-appearance: none!important;
  width:40px;
  height:40px;
  -webkit-border-radius:6px;
     -moz-border-radius:6px;
          border-radius:6px;
  font:2em 'Open Sans';
  text-align:center;
}

.check:after {
  position:absolute;
  top:9px;
  left:8px;
  content:"";       background:url('http://static.tumblr.com/upanoab/0hOmmcbuh/tick-sprite.png');
  width:22px;
  height:22px;
}

.check:checked:after {
  position:absolute;
  top:9px;
  left:6px;
  content:"";       background:url('http://static.tumblr.com/upanoab/0hOmmcbuh/tick-sprite.png');
  background-position:-20px;
  width:22px;
  height:22px;
}


/* Default Circle Checkbox
===============================*/
.circles {
  position:relative;
  -webkit-appearance: none;
  width:40px;
  height:40px;
  -webkit-border-radius: 100px;
  -moz-border-radius: 100px;
  border-radius: 100px;
  margin:8px;
}

.circles:after {
  position:absolute;
  left:8px;
  top:9px;
  content:"";
 background:url('http://static.tumblr.com/upanoab/0hOmmcbuh/tick-sprite.png');
  width:22px;
  height:22px;
}

.circles:checked:after {
  position:absolute;
  left:8px;
  top:9px;
  content:"";
 background:url('http://static.tumblr.com/upanoab/0hOmmcbuh/tick-sprite.png');
  background-position:-23px;
  width:22px;
  height:22px;
}

/* Radio Elements
===============================*/
.radio {
  position:relative;
  -webkit-appearance:none;
  width:30px;
  height:30px;
  margin:10px;
  margin-top:0px;
  -webkit-border-radius:100px;
     -moz-border-radius:100px;
          border-radius:100px;
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

.radio:checked {
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

.radio:checked:after {
  position:absolute;
  top:5px;
  left:5px;
  width:20px;
  height:20px;
  background:#fff;
  content:"";
  -webkit-border-radius:100px;
     -moz-border-radius:100px;
          border-radius:100px;
}

/* Search Elements
===============================*/
.search {
  padding:10px;
  width:300px;
  display:block;
  margin:0 auto;
  margin-bottom:10px;
  -webkit-border-radius:6px;
     -moz-border-radius:6px;
          border-radius:6px;
  border:none;
  color:#fff;
  outline:none;
}

.search:focus {
  background:#fff;
  border:2px solid #34495E;
  color:#34495E;
  font-weight:600;
}

.search::-webkit-input-placeholder {
   color: #FFF;
}

.search:-moz-placeholder { 
   color: #FFF;
}

.search::-moz-placeholder {
   color: #FFF;
}

.search:-ms-input-placeholder {  
   color: #FFF;
}

/* Dropdown Menu
===============================*/
.drop-wrap {
  width:300px;
  margin:0px auto;
}

.main-drop {
  position:relative;
  width:300px;
  background:#3498DB;
  padding:10px 10px 15px 20px;
  -webkit-border-radius:6px;
     -moz-border-radius:6px;
          border-radius:6px;
  text-align:left;
  font-weight:400;
  color:#fff;
  cursor:pointer;
}

.main-drop span {
  position:absolute;
  top:0;
  right:0;
  padding:12px 10px 8px 10px;
  background:#2980B9;
  -webkit-border-top-right-radius: 6px;
  -webkit-border-bottom-right-radius: 6px;
     -moz-border-radius-topright: 6px;
     -moz-border-radius-bottomright: 6px;
          border-top-right-radius: 6px;
          border-bottom-right-radius: 6px;
  cursor:pointer;
}

.main-drop span:hover {
  background:#2675a9;
}

.drop-wrap ul {
  list-style:none;
  text-align:left;
  display:none;
  width:300px;
  background:#34495E;
  padding:0;
  -webkit-border-radius:6px;
     -moz-border-radius:6px;
          border-radius:6px;
  overflow:hidden;
}

.drop-wrap li {
  display:block;
  color:#fff;
  font-size:0.8em;
  padding:10px 10px 10px 18px;
  cursor:pointer;
}


.drop-wrap li:hover {
  background:#3498DB;
  cursor:pointer;
}

/* Range Elements
===============================*/
input[type='range'] {
   position: absolute;
   right: 10px;
   left: 10px;
   width:300px;
   -webkit-appearance: none;
   -webkit-border-radius: 5px;
      -moz-border-radius: 5px;
           border-radius: 5px;
   background: #34495E;
   height: 10px;
   margin: 0px auto;
   transition: all .3s ease-in-out;
   -moz-transition: all .3s ease-in-out;
   -webkit-transition: all .3s ease-in-out;
}

 input[type='range']::-webkit-slider-thumb {
  -webkit-appearance: none;
  -webkit-border-radius: 100px;
  -moz-border-radius: 100px;
  -webkit-border-radius: 100px;
  background-color: #1ABC9C;
  height: 20px;
  width: 20px;
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

input[type='range']::-webkit-slider-thumb:active {
  padding:11px;
  transition: all .3s ease-in-out;
  -moz-transition: all .3s ease-in-out;
  -webkit-transition: all .3s ease-in-out;
}

UI-Kit.markdown

UI Kit

Free to use. Doesn't work in Firefox, contributions are appreciated. (Navigation, Dropdowns, Checklist, Input, Search & Range)

I used this, for the colors.

Forked from Joe Richardson's Pen UI Kit.

A Pen by Captain Anonymous on CodePen.

License.