Should i check in all? or in any one is enough because all share same rendering engine Webkit.
My question is related to HTML CSS rendering.
I know one difference Safari for windows and MAC both have Font smoothing (anti -alisaing)
Is there any other differences?
There's definitely a difference between Chrome and Safari due to Safari's font rendering. In Safari text tend to be a bit bolder due to the anti-aliasing algorithm and can sometimes take up a few extra pixels on the screen.
Also keep in mind that Safari uses the SquirrelFish javascript engine while Chrome uses V8.
I would check, yes.
Whilst the browsers all use the same rendering core, they're not necessarily on the same version (and there are multiple versions of Safari out there in any case).
Also, as slebetman says, font rendering is quite different depending on OS and anti-aliasing settings too, so you need to be aware of that.
There are major and minor differences. Do check!
Minor: full support for CSS3 border-radius in Chrome. I've read about, but can't find, this in Safari.
Huge: zooming in Chrome zooms everything. (This is the behavior in almost every browser.) Zooming Safari zooms text but leaves other things unchanged. Your ever-so-carefully-laid-out form is highly likely to be trashed if the user zooms in. Leave lots of extra space.
Shadows are fast&ugly in chome; slower&prettier in safari (and firefox). IIRC there was some difference in CSS3 transitions too - but really, these details are still in flux anyhow and change from version to version.
In practice, I only check one of the two regularly, which is generally fine. Before putting major changes online, it's obviously not a bad idea to check again, but during development, it's not worth the hassle; they're so similar anyhow...