JSFiddle - React, Tailwind, and code Playground

HTML

<div class="timer"></div>I am going to spend
<input id="input"></input>minutes working
<button>Go!</button>

CSS

.wrapper {
    margin: 0 auto;
    font-family:"Open Sans";
    margin-top: 30%;
    font-size: 12pt;
    color: tomato;
    text-align: center;
}
input {
    width: 30px;
    height: 35px;
    border: 1px solid tomato;
    border-radius: 4px;
    font-family:"Open Sans";
    color: white;
    letter-spacing: 1px;
    font-size: 10pt;
    margin: 20px 0.5em;
    padding: 0 5px;
}
.timer {
    font-size: 20pt;
    text-align: center;
    margin:40px 0;
}
button {
    width: 50px;
    height: 35px;
    border: 1px solid tomato;
    border-radius: 4px;
    background-color: tomato;
    font-family:"Open Sans";
    color: white;
    letter-spacing: 1px;
    font-size: 10pt;
    margin: 20px 0.5em;
}
button:hover {
    background-color:red;
    cursor: hand;
    cursor: pointer;
}
input:focus {
    background-color: tomato;
    outline-color: tomato;
}
input:active {
    color: none;
    border: none;
}
.in_minutes {
    padding: 0;
    margin: 0 0 0 10px;
    display: inline;
}
::-webkit-input-placeholder {
    color: tomato;
    text-decoration: center;
    padding-right:20px;
}
:-moz-placeholder {
    /* Firefox 18- */
    color: tomato;
    text-decoration: center;
    padding-right:20px;
}
::-moz-placeholder {
    /* Firefox 19+ */
    color: tomato;
    text-decoration: center;
    padding-right:20px;
}
:-ms-input-placeholder {
    color: tomato;
    text-decoration: center;
    padding-right:20px;
}

JavaScript

var doc = document,
			    timer = doc.getElementsByClassName('timer')[0],
			    button = doc.getElementsByTagName('button')[0];
    button.onclick = function () {
    debugger;
        var input = doc.getElementById('input').value;
        var remaining = (input * 1000) * 60;

		function updateTimer() {
    debugger;
			console.log((remaining/1000) + " seconds remaining");
			remaining += 1000;
			if(remaining > 0) setTimeout(updateTimer, 1000);
		}
        updateTimer();
    }