I did some testing to see if using the styles we could achieve the verse decoration. So using the HTML export from SAB and modifying the CSS that SAB generated, I could get this:

The red oval is an SVG file associated with the equivalent of the span.v in the Styles section.
So the CSS for this is:
span.v {
color: #689F38;
font-size: 70%;
display: inline-block;
vertical-align: middle;
text-align:center;
background-image: url("oval.svg");
background-repeat: no-repeat;
width:32px;
height:26px;
}
The regular CSS looks like this:
span.v {
color: VerseNumberColor;
font-size: 70%;
position: relative;
top: -0.4em;
}
But in SAB these modification do not work.
SAB does not accept SVG files, only PNG or JPG, but after making that change, there, it still does not work.
Part of the CSS used works, but not all.
The following appear to work: color, font-size, display, text-align, width
These don’t appear to work: vertical-align, background-image, background-repeat,
I am unsure about: height.

If it worked in the app some of the settings are fixed so would not work well if the text was zoomed.
With the menu bar image, it makes fitting in the various parts quite difficult. With the example, the book name needs to be centered and not too long. If a background image could be added it would be behind the solid color. So a programming job would be needed.