mobi to epub conversion - how do I change the img settings?

[paola]

First of all, I'd like to thank again Kovid and the other collaborators for the great service you offer with Calibre!

Now for my question: while, converting mobi to epub (though I suspect this might apply more generally) as far as I can see Calibre sets images width and height to auto. I would like instead to "manipulate them" by setting e.g. width: 75%.

Since in this specific epub calibre put the image class as .calibre3, after generating the epub I erased it and put as extra css in the "common options" (in Preferences\conversion) the code:

.calibre3 {
    height: auto;
    width: 75%
    }

but unfortunately this is ignored. I can of course explode the epub and change the css file directly, but I'd love to be able to do this automatically in Calibre upon conversion: is this possible?