index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <!-- <title>Temperature Converter</title> -->
    <link rel="stylesheet" href="style.css" />
</head>

<body>
    <div id="box">
    <h1 id="headeris"><em>Temperature Converter</em></h1>
    <!-- <h1 id="headern">Celsius to Fahrenheit</h1> -->
    <div id="main_div">

        <div id="container">
            <form name="calculator" onsubmit="myfun();return false;">
               <div id="column">
                    <div id="row">
                    <label>Degrees </label><br>
                    <input type="text" id="temp" name="temp" >
                    </div>
                    
                    <div id="row">
                    <label>Type </label><br>
                <select id="select_temp" name="select_temp" id="select_temp">
                    <optgroup label="Temperature">
                    <option value="Celcius" name="celcius">Celcius</option>
                    <option value="Fehranheit" name="fahrenheit">Fahrenheit</option>
                </optgroup>
                </select>
                    </div>
                    </div>
                <br>
                <div id="row">
                    <label>Result </label><br>
                <div id="resultcontainer">
                    <span id="myresult"></span>
                </div></div>
                <br /><br />
                <input type="submit" id="btn1" value="Convert" />
            </form>

        </div>

        
    </div>
</div>
</body>
<script src="script.js"></script>
</html>