JSFiddle - React, Tailwind, and code Playground

HTML

<span>距除夕还有</span><div class="day">
    <span class="fir"></span>
    <span class="sec"></span>
</div>
<span>天</span>
<div class="hour">
    <span class="fir"></span>
    <span class="sec"></span>
</div>
<span class="split">:</span>
<div class="minute">
    <span class="fir"></span>
    <span class="sec"></span>
</div>
<span class="split">:</span>
<div class="second">
    <span class="fir"></span>
    <span class="sec"></span>
</div>

CSS

.day,.hour, .minute, .second{
    display:inline-block;
    color:#fff;
}

.split{
    display:inline;   
}

.in_0{background:#f00;}
.in_1{background:#e00;}
.in_2{background:#d00;}
.in_3{background:#c00;}
.in_4{background:#b00;}
.in_5{background:#a00;}
.in_6{background:#900;}
.in_7{background:#800;}
.in_8{background:#700;}
.in_9{background:#600;}

JavaScript

var deadLine = new Date('2014-1-30 23:59:59').getTime();
var $hour = $('.hour');
var $minute = $('.minute');
var $second = $('.second');
var $day = $('.day');

function updateTime(){
    var now = new Date().getTime();
    
    var diff = deadLine - now;
    
    if(diff <= 0){
        clearInterval(timer);
        return;
    }
    var second = parseInt(diff / 1000);
    var diffDay = parseInt(second / (60 * 60 * 24));
    var diffHour = parseInt(second / 60 / 60) % 24;
    var diffMinute = parseInt(second % (60 * 60) / 60);
    var diffSecond = second % 60
    
   
    setValue($day, diffDay);

    setValue($hour, diffHour);
    
    setValue($minute, diffMinute);
    
    setValue($second, diffSecond);
}

function setClass(parent, value){
    value = getSplitNumber(value);
    parent.find('.fir').attr('class', 'fir').addClass(getClassFromValue(value[0]));
    parent.find('.sec').attr('class', 'sec').addClass(getClassFromValue(value[1]));
}

function setValue(parent, value){
    parent.find('.fir').html(getSplitNumber(value)[0]);
    parent.find('.sec').html(getSplitNumber(value)[1]);
    
    setClass(parent, value);
}

function getClassFromValue(value){
    return 'in_' + value;
}

function getSplitNumber(value){
    if(value > 9){
        return value.toString();
    }else{
        return '0' + value;
    }
}

var timer = setInterval(function(){
    updateTime();
}, 1000);