If ADE is ignoring the style sheet, it probably means there's an error somewhwere in the CSS. You can check it
here.
Whereas Sigil and some readers are more tolerant of CSS errors, ADE will disregard the entire CSS file if contains so much as a single misplaced semicolon.
And many stand-alone readers are based on the ADE engine.
Oops. Theducks beat me to it.