I'm sure there are members who have worked with CSS. As I prefer to work with CSS and not WYSIWYG editors in building HTML sites, I recognize it immediately. An example being:
.appstore {
width:100% !important; Use 100% of container width - i.e. display full width.
float: left !important; Element should be set to the left - i.e. display photo on left with text on right.
padding: 10px 0 10px 0 !important; Sets space 'within' a container - i.e. white-space 10px top, 0px right, 10px bottom, 0px left.
display: block !important; Tells to display text or graphics on separate line - i.e. display photo on separate line.
margin:0 auto !important; Tells to use 100% of container width and height; auto centers block not the elements within container - i.e. no white space outside the border area.
You would generally use this within <div> container tag which would format the elements with the above mentioned:
<div class="appstore">
...some text or graphics...
</div>
My guess is that since you're seeing CSS text, the <style> tags were placed in the wrong place or missing in the HTML email.