Drilldown

<form name="form1" id="form1" action="/action_page.php">
            <label for="subject">Subjects:</label>
            <select class="ss-c-select" style="max-width: 320px" name="subject" id="subject">
                <option value="" selected="selected">Select subject</option>
            </select>
            <br />
            <br />
            <label for="topic">Topics:</label>
            <select class="ss-c-select" style="max-width: 320px" name="topic" id="topic">
                <option value="" selected="selected">
                    Please select subject first
                </option>
            </select>
            <br />
            <br />
            <label for="chapter">Chapters:</label>
            <select class="ss-c-select" style="max-width: 320px" name="chapter" id="chapter">
                <option value="" selected="selected">
                    Please select topic first
                </option>
            </select>
            <br />
            <br />
            <button type="submit" class="ss-c-button ss-c-button--primary">Submit</button>
        </form>