How to make a placeholder for a 'select' box

For example:

<select>
    <option value="1">C#</option>
    <option value="2">C++</option>
</select>

If you want to add a placeholder to select for example: '--- Select ---'

You can modify your html as shown below.

<select>
    <option value="" disabled selected>--- Select ---</option>
    <option value="1">C#</option>
    <option value="2">C++</option>
</select>