สอบถามคำสั่ง วิธีทำปุ่ม เพิ่มลดขยายตัวอักษร เปลี่ยนสีเว็บไซต์ คะ.

    <button onclick="document.body.style.fontSize = '14px'">14px</button>
    <button onclick="document.body.style.fontSize = '16px'">16px</button>
    <button onclick="document.body.style.fontSize = '18px'">18px</button>
    <button onclick="document.body.style.backgroundColor = 'red'">red</button>
    <button onclick="document.body.style.backgroundColor = 'green'">green</button>
    <button onclick="document.body.style.backgroundColor = 'blue'">blue</button>
    <p>
      Lorem ipsum dolor sit amet
    </p>

<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script type="text/javascript" src="jquery-calx-1.1.8.min.js"></script>
<form id="calx">
<table>
<tbody>
<tr>
<td>Processor :</td>
<td><select name="proc" id="proc">
<option value="15">1 Core</option>
<option value="22">2 Core</option>
<option value="30">4 Core</option>
</select></td>
</tr>
<tr>
<td>RAM :</td>
<td><select name="ram" id="ram">
<option value="5">1 GB</option>
<option value="8">2 GB</option>
<option value="15">4 GB</option>
<option value="25">8 GB</option>
<option value="30">10 GB</option>
</select></td>
</tr>
<tr>
<td>HDD Space :</td>
<td><select name="hdd" id="hdd">
<option value="5">250 GB</option>
<option value="7">500 GB</option>
<option value="12">750 GB</option>
<option value="15">1 TB</option>
<option value="25">2 TB</option>
</select></td>
</tr>
<tr>
<td>Price per Month :</td>
<td><span id="price" data-format="$ 0,0[.]00" data-formula="$hdd+$proc+$ram"></span> /Month</td>
</tr>
<tr>
<td>Contract :</td>
<td><input type="text" id="contract" data-format="0" style="width: 40px" value="12" />
Month(s)</td>
</tr>
<tr>
<td>Total Price :</td>
<td id="total_price" data-format="$ 0,0[.]00" data-formula="$contract*$price"></td>
</tr>
</tbody>
</table>
</form>
<script type="text/javascript">
$(document).ready(function(){
    $('#calx').calx({});
});
</script>> 

<script src="//code.jquery.com/jquery-1.11.3.min.js"></script>
<script src="jquery.dynaprice.min.js"></script>
<input type="number" id="demo" min="1" max="100" step="1" name="quantity" value="1">
$ <span id="price"></span>
$('input#demo').dynaprice({
  destination: $('span#price')
});
// jQuery selector for price calculator
destination : $('.js-dnp-destination'),

// event to bind
bind : 'change',

// auto initialization
autoInit : true,

// unit price
cost : 3,

// callbacks
beforeUpdate : null,
afterUpdate : null,

<script src="//code.jquery.com/jquery.min.js"></script>
<script src="jquery.formula.js"></script>

<input type="text" data-variavel="field1">
<input type="text" data-variavel="field2">

<input type="text" data-formula="#field1# + #field2#">

<input type="text" data-formula="#field1# * #field2#">