对齐图像中心，响应div的底部

<div id="banner" class="cf">
        <div class="banner container">
            <hr/>
            <p class="banner-text">
            Some text here
            <span class="sub-bt">That's it.</span>
            </p>
            <a href="/go.html?url=#" rel="nofollow" class="learn-btn">Learn More</a>

            <img src="<?php echo get_template_directory_uri(); ?>/library/images/responsive_ex.png" class="res-ex">
        </div>
    </div>
<div id="banner" class="cf">
        <div class