body {
            font-family: sans-serif;
        }
        
        body, html {
            margin:0; 
            padding:0;
        }
        * {
            box-sizing: border-box;
        }
        
        #top {
            overflow: auto;
            padding: 0 30px;
            background: #efefef;
            border: 1px solid grey;
        }
        
        h1 {
            float: left;
            font-size: 120%;
        }
        
        #nav {
            width: 350px;
            margin: 0.97em auto;
        }

        #nav li {
            float: left;
            list-style: none;
        }
        
        #nav li a {
            text-decoration: none;
            padding: 7px 10px;
            color: #333;
            border: 1px solid #ccc;
            border-right-width: 0;
            background: transparent;
            font-size: 90%;
        }
        
        #nav li:first-child a {
            border-top-left-radius: 4px;
            border-bottom-left-radius: 4px;
        }
        
        #nav li:last-child a {
            border-right-width: 1px;
            border-top-right-radius: 4px;
            border-bottom-right-radius: 4px;
        }
        
        #panels {
            width: 100%;
            overflow: auto;
        }
        
        .panel {
            float: left;
            width: 25%;
            border: 1px solid #666;
            border-top-width: 0;
            position: relative;
            display: none;
            height:  500px;
        }
        .panel + .panel {
            border-left-width: 0;
        }
        
        #panels textarea{
            position: relative;
            display:block;
            width: 100%;
            height: 100%;
            border: none;
            resize: none;
        }

        .html #html,
        .css #css,
        .js #js,
        .output #output {
            display: inline-block;
        }
        
        .html #nav a[href="#html"],
        .css #nav a[href="#css"],
        .js #nav a[href="#js"],
        .output #nav a[href="#output"] {
            background: #f6f9ff;
        }
        
        #player #nav li a:hover {
            background-color: lightgrey;
        }