I export with my custom Leuven theme (a light theme) css and it works fine.
I also have my emacs theme as a dark theme by default.

;; (setq org-html-htmlize-output-type 'inline-css) ; default
(setq org-html-htmlize-output-type 'css)
;; (setq org-html-htmlize-font-prefix "") ; default
(setq org-html-htmlize-font-prefix "org-")

Check out this link for the full solution including Leuven theme css:
http://emacs.stackexchange.com/a/7633/115

--
Kaushal Modi
On Aug 2, 2015 9:19 AM, "Rick Frankel" <rick@rickster.com> wrote:

> On Sun, Aug 02, 2015 at 10:24:25AM +0100, Eric S Fraga wrote:
> > Now, I can simply start up emacs with a light background, export my
> > slides and everything is fine.  However, it would be nice to not have to
> > start up a new emacs just for this.  Is there an easy way to pretend,
> > for export to HTML, that emacs is using a light background?  Maybe a way
> > to advise the exporter?
>
> > PS - ideally, code export to HTML would make use of CSS instead of
> >      hard-coding in the colours but that's a discussion for another
> >      day...
>
> Check the documentation for the variable `org-html-htmlize-output-type'.
> Since
> ox-reveal is derived from ox-html, it should work as specified. I
> personally
> use ox-deck (also derived from html), so YMMV.
>
> rick
>
>