<!DOCTYPE html>
<html lang="en">
    <head>
        <link rel="stylesheet" type="text/css" href="calculator.css"/>
    </head>
    <body>
        <div id="dest">
        </div>
        <div id="calculator">
            <div id="c_title">
                <h2 id="c_title">Test Observe
                    <br/>
                    <span id="msg">btn click
                    </span>
                </h2>
                <p>this is after observe
                </p>
                <div>content</div>
          