HTML/CSS - Custom input box Online Editor and JavaScript Compiler

html

<!DOCTYPE html>
<html>
    <head>
        <title>Page Title</title>
        <meta name="description" content="Custom input box">
        <meta name="keywords" content="custom, input box, prompt">
        <meta name="author" content="Calvin - https://www.sololearn.com/Profile/4354920">
        <meta name="copyright" content="Calvin">
        <meta name="date" content="2017-1021" scheme="YYYY-MM-DD">
        <meta name="revised" content="" scheme="YYYY-MM-DD">
        
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
    </head>
    <body>
        <div class="cbox">
            <div class="inputbox">
                <form name="form">
                    <h3>Code Playgound</h3>
                    <h5 class="qtn"></h5>
                    <label>Input</label>
                    <input class="input" />
                    <div class="btns">
                        <button class="cancel" onclick="onCancel(event)">CANCEL</button>
                        <button class="ok" onclick="onOk(event)">OK</button>
                    </div>
                </form>
            </div>
        </div>

css

/**
 * @title   Custom input box
 * @version   0.1
 * @package   xhtml-css
 * @author    Calvin
 * @copyright 2017 by the author
 * @cssdoc    version 1.0-pre
 * @license   GPL v3
*/
body {
    margin: 0;
    padding: 0;
}
.cbox {
    display: none;
    position: absolute;
    top: 0;
    bottom: 0;
    width: 100vw;
    height: 100vh;
    z-index: -99;
}
.inputbox {
    padding: 20px;
    width: 80%;

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