[Tex2002ans]

Originally Posted by Capricorn

I have a tendency to simply remove such entries as they never seem to impact anything, at least in my experience.

Depends on what the CSS is!

For example, here is a topic about testing some selectors in CSS3:

https://www.mobileread.com/forums/sho...d.php?t=212300

Originally Posted by Capricorn

However, if I leave them there, would that cause problems?

Again, it depends on what the CSS3 is doing exactly. In the CSS standard, if the device doesn't recognize a given CSS property, it will completely ignore it.

For example, in Doitsu's EPUB example in the thread linked above, there is this code:

<h3>Capitulum Unum</h3>

with this CSS:

h3 {
    font-family: sans-serif;
    font-size: 2em;
    text-align: center;
    text-transform: uppercase;
    text-shadow: 2px 2px 3px grey;
    transform: rotate(-3deg);
    -webkit-transform: rotate(-3deg);
}

Many devices don't know "text-transform: uppercase", so the fallback will show "Capitulum Unum" instead of appearing as "CAPITULUM UNUM".

If the device doesn't understand "transform: rotate(-3deg)", the chapter title will not be rotated a few degrees, but will stay horizontal.

(Similarly with the "text-shadow: 2px 2px 3px grey" showing shadows showing behind the text).

The book will still be completely readable/understandable without this fluff.

But, let us say you wrote a book in which every odd paragraph is blue, and every even paragraph is red ("nth-child(odd)" + "nth-child(even)"). All of a sudden, if the device doesn't implement that CSS3, your book will not be understandable when read on a CSS2 device.

Originally Posted by Capricorn

And if one day epub 3 takes the upper hand, would that be detrimental to those files. I understand epub 3 uses CSS3 but epub 2 uses CSS2.1.

And remember, EPUBs only support a subset of all CSS2.1. Similarly, EPUB3 devices will only support a subset of CSS3.

For example, I doubt CSS3 Animations/Transitions are going to be on e-ink EPUB3 readers:

http://www.w3schools.com/cssref/css3_pr_animation.asp

Something like iBooks might be able to run those animations (not that they really follow the EPUB standards in the first place), but I wouldn't be completely reliant upon it. It is just always a good idea to keep in mind the fallbacks.