Result

jQuery

    $("ol li").each(function (i) {
        //要素の数を取得
        i = i+1;
        //要素の頭に数値を加える
        $(this).prepend('<span class="number"> No.'+i+'</span>');
   });

css

.number{
    color:red;
    display:inline-block;
    margin-right:15px;
    font-size:20px;
}
ol{margin:25px;}
li{margin-bottom:15px;}

html

<ol>
    <li>list</li>
    <li>list</li>
    <li>list</li>
    <li>list</li>
    <li>list</li>
</ol>

via

jQuery Sequential List

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