<fieldset>
    <legend>Choose some monster features</legend>

    <div>
        <input type="checkbox" id="scales" name="feature"
               value="scales" checked />
        <label for="scales">Scales</label>
    </div>

    <div>
        <input type="checkbox" id="horns" name="feature"
               value="horns" />
        <label for="horns">Horns</label>
    </div>

    <div>
        <input type="checkbox" id="claws" name="feature"
               value="claws" />
        <label for="claws">Claws</label>
    </div>

</fieldset>

Output