  <!-- btn-nav -->
    <h2>btn-nav</h2>
    <button class="btn-nav">btn-nav</button>
    <button class="btn-nav btn-small">btn-nav</button>
    <button class="btn-nav btn-medium">btn-nav</button>
    <button class="btn-nav btn-large">btn-nav</button>
    <button class="btn-nav btn-mega">btn-nav</button>
    <br />
    <br />
    <!-- btn-alt -->
    <h2>btn-alt</h2>
    <button class="btn-alt">btn-alt</button>
    <button class="btn-alt btn-small">btn-alt</button>
    <button class="btn-alt btn-medium">btn-