<h1>        CSS Counter Game</h1>    <section>        <h2>            Pick the numbers that add up to 72:</h1>            <input id="a" type="checkbox"><label for="a">64</label>            <input id="b" type="checkbox"><label for="b">16</label>            <input id="c" type="checkbox"><label for="c">-32</label>            <input id="d" type="checkbox"><label for="d">128</label>            <input id="e" type="checkbox"><label for="e">4</label>            <input id="f" type="checkbox"><label for="f">-8</label>            <span class="sum"></span>    </section>

 body        {            counter-reset: sum;        }                #a:checked        {            counter-increment: sum 64;        }        #b:checked        {            counter-increment: sum 16;        }        #c:checked        {            counter-increment: sum -32;        }        #d:checked        {            counter-increment: sum 128;        }        #e:checked        {            counter-increment: sum 4;        }        #f:checked        {            counter-increment: sum -8;        }                .sum::before        {            content: ‘= ‘ counter(sum);        }                /* the rest is just to make things pretty */                body        {            margin: 32px;            font: 700 32px/1 ‘Droid Sans‘ , sans-serif;            color: #fff;            background-color: #583f3f;        }                h1        {            margin: 0 0 32px;            font-size: 48px;        }                h2        {            margin: 0 0 8px 8px;            font-size: inherit;        }                section        {            margin-bottom: 16px;            padding: 16px;            border-radius: 4px;            overflow: hidden;            background-color: rgba(255, 255, 255, .1);        }                input        {            position: absolute;            left: -9999px;        }                label        {            float: left;            margin: 8px;            padding: 16px;            border-radius: 4px;            border: solid 2px rgba(255, 255, 255, .4);            background-color: rgba(255, 255, 255, .2);            cursor: pointer;            transition: all .1s;        }                label::before        {            display: inline;        }                input:checked + label        {            border: solid 2px #fff;            background-color: rgba(255, 255, 255, .4);            box-shadow: 0 0 10px #fff;        }                span        {            float: left;            margin: 8px;            padding: 18px;            border-radius: 4px;            background-color: rgba(0, 0, 0, .1);        }                #a:checked ~ #b:checked ~ #c:not(:checked) ~ #d:not(:checked) ~ #e:not(:checked) ~ #f:checked ~ .sum::after        {            content: ‘ (hooray!)‘;        }