JSFiddle - React, Tailwind, and code Playground

HTML

<div id="register">
            <div id="IP" class="box">
                <p>IP</p>
            </div>
            <div id="IS" class="box">
                <p>IS</p>
            </div>
            <div id="R0" class="box">
                <p>R0</p>
            </div>
            <div id="R1" class="box">
                <p>R1</p>
            </div>
        </div>
        <div id="case">
            <div id="0" class="box">
                <p>0</p>
            </div>
            <div id="1" class="box">
                <p>1</p>
            </div>
            <div id="2" class="box">
                <p>2</p>
            </div>
            <div id="3" class="box">
                <p>3</p>
            </div>
            <div id="4" class="box">
                <p>4</p>
            </div>
            <div id="5" class="box">
                <p>5</p>
            </div>
            <div id="6" class="box">
                <p>6</p>
            </div>
            <div id="7" class="box">
                <p>7</p>
            </div>
            <div id="8" class="box">
                <p>8</p>
            </div>
            <div id="9" class="box">
                <p>9</p>
            </div>
            <div id="10" class="box">
                <p>10</p>
            </div>
            <div id="11" class="box">
                <p>11</p>
            </div>
            <div id="12" class="box">
                <p>12</p>
            </div>
            <div id="13" class="box">
                <p>13</p>
            </div>
            <div id="14" class="box">
                <p>14</p>
            </div>
            <div id="15" class="box">
                <p>15</p>
            </div>
        </div>

CSS

body {
    background-color: dimgrey;
}
p{
    display: table-cell;
    text-align: center;
    line-height: 100px;
    font-size: 40px;
    width: 100px;
    font-family: Verdana, Geneva, sans-serif;    
}
 
#register{
    border: 2px solid black;
    width: 102px;
    float: left;
    margin: 0 0 0 250px;
}
 
#case {
    border: 2px solid black;
    width: 420px;
    margin: 80px auto;
    /*height: 420px;*/
}
 
.box {
    display: none;
    width: 100px;
    height: 100px;
    background-color: lightgrey;
    border: 1px solid black;
    margin: 0;
}