HTML positioning attributes are not compatible with CSS; therefore, by default, DITA2Go omits these attributes for HTML output. Use the positioning properties available in format configuration files instead; see §7. Configuring output formats.
§32.4.3 Omitting paragraph tags around graphics
When you use CSS, you can center graphics with DITA2Go macros. For example, to center all images:
[GraphStartMacros] * = <div class="img">
[GraphEndMacros] * = </div>
See §32.4.2 Replacing or surrounding a graphic with macro code.
div.img {text-align: center; }
Or, if DITA2Go maintains CSS for your project (see §31.8.3 Overriding styles in DITA2Go-generated CSS files):
[CSSEndMacro] div.img {text-align: center; }
You have to use <div> because CSS applies text-align only to block elements, and <img> is not a block element.
To add a space above an image:
[GraphStartMacros] GraphicID = <br>