The Sublime Editor basic window in CSS/HTML/JS

You can maximise it too with the buttons, it's also responsive

Sublimey Text

HTML Example


<ul>
   <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
   <li>Aliquam tincidunt mauris eu risus.</li>
   <li>Vestibulum auctor dapibus neque.</li>
</ul>

Javascript File

function Class(){
    this.method = function(){alert('simple method')};
}​​​​​​​​​
// some random JS
var object = new Class();
object.method();​

CSS File

position: fixed;
top: 0;
right: 0;
width: 100%;

font-family: "Source Code Pro", Consolas, "Courier New", monospace;
font-size: 1em;
font-weight: 400;
z-index: 40;

background: 
    linear-gradient( 
        to top , 
        rgba(255,255,255,0.8), 
        rgba(255,255,255,0.6) 
    );

box-shadow: 
    inset 0 -1px 1px rgba(255,255,255,1), 
    inset 0 -3px 3px rgba(255,255,255,0.7), 
    0 0 20px rgba(0,0,0,0.2);