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">
    <link rel="stylesheet" href="style.css">
    <title>Temperature Converter</title>
</head>
<body>
    <form id="tempCalc" onsubmit="calculateTemp(); return false">

        <label for="temp">Enter the temperature to convert</label>
       <br /> <input type="number" name="temp" id="temp">
    
        <select name="temp_diff" id="temp_diff">
            <option value="cel">° Celcius</option>
            <option value="fah">° Fahrenheit</option>
        </select> <br />
    
        <input type="submit" name="temp"> <br />
    
        <span id="resultContainer"></span>
    </form>    
    <script src="index.js"></script>
</body>
</html>