input输入的文字比placeholder 大很多时，plac

<script type="text/javascript">
        function aa(event) {
            var Oinput = document.getElementById('amount');
            Oinput.style.fontSize=36+'px';
            Oinput.placeholder='';

        }
        function bb(event) {
            var Oinput = document.getElementById('amount');
            Oinput.style.fontSize=13+'px';
            Oinput.placeholder='pls enter ur name';
        }
    </script>

    <input type="text" class="amount" id="amount"  
       placeholder="pls enter ur name"  
       onfocus="aa(event)" onblur="bb(event)">

Paste_Image.png Paste_Image.png