css counter

css counter is css3, only effective in modern browsers
counter-reset: Set the value of the counter for the number of occurrences of a certain selector. Default is 0. Just define a counter, you can define the initial value, the default is 0

counter-increment: Set the counter increment each time a selector appears. The default increment is 1.

demo

#css implements counting and

css

 body{
            margin: 0;
            counter-reset: increment;
        }
        input{
            border: none;
            margin: 0;
            padding: 0;
        }
        .number1 input[type=checkbox]:checked{
            counter-increment:increment 20;
        }
        .number2 input[type=checkbox]:checked{
            counter-increment:increment 30;
        }
        .number3 input[type=checkbox]:checked{
            counter-increment:increment 40;
        }
        .number4 input[type=checkbox]:checked{
             counter-increment:increment 50;
         }
        .number5 input[type=checkbox]:checked{
            counter-increment:increment 60;
        }
        .sum:after{
            content: counter(increment);

        }

html

<label class="number1"><input type="checkbox">20</label>+<label class="number2"><input type="checkbox">30</label>+<label class="number3"><input type="checkbox">40</label>+<label class="number4"><input type="checkbox">50</label>+<label class="number5"><input type="checkbox">60</label>=<p class="sum"></p>

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