New HTML5 and CSS3 introduced lot of new features,although it is not completely supported by most of the browsers.Is it a good idea to design a website using HTML5 and css3?
and for browsers which not support HTML5 display low bandwidth version of it?
or there exists any library's(js) to fix HTML5 and CSS3 comparability for browsers like IE 6 or Firefox 3?
I think it's very good idea. There is a nice js library called modernizr which can add the support of html5 new tags and detect which css3 features the browser supports.
It is a good idea to use these new technologies, because it's where we're headed. So many other sites already have content that requires a modern browser. Take Youtube for example. Even Gmail. But the list goes on. Most people have a modern browser already, and it would be to YOUR full advantage to design a site with HTML5 and CSS3. While support for some features is not uniform yet across browsers, the general idea is there. There's no reason for you to waste your effort making an "old-browser-friendly" site since they are a dying breed: large companies with technology contracts or plans where upgrades haven't kicked in, or old family computers that physically can't handle the new operating systems and browsers. See this chart: http://gs.statcounter.com/#browser_version_partially_combined-ww-monthly-201107-201207
Of course you may want to put up banners like this: http://www.updateyourbrowser.net/en/ (scroll to bottom, click "view example") to inform your outdated clients that they can't get the full experience from your site without first upgrading. "That some features may be unavailable." You can also try to adapt certain "coping methods" based on user-agent, so that old browsers automatically get a non-CSS3 stylesheet, and so forth.
Yes I would design with HTML5 and CSS3 to save time you can use some scripts such as video players which start with HTML5 and have safe fall backs for any browser which doesn't support .
I'd also start with a framework such as Twitter bootstrap which is very compliant, you'll save a lot of time messing with CSS.
HTML5 is mostly ok but i think CSS3 is not officially announced as finished and there are some risks. Yes, most of us are using modern browsers but css3 standarts are not even fully compatible between them. Mozilla Chrome IE and Opera are not using the whole css3 syntax same. This is really annoying me as a web developer i hate things those are not certain and not having borders well described.
So, please W3C, finish css3 development to end our pain as soon as possible. You can version it later just draw the borders at the stage.
You can take a look at browser compatibility chart here ;
I agree with ionFish that it's a good idea to use these new technologies, but you should keep your users on your mind all time when you're writing the codes.
Like many other users here, I have most recent versions of different web browsers too, but I mainly use Firefox, sometimes Chrome, and rarely the IE. When I started making my first website, I used some super cool and super easy codes to build a lightweight and yet beautiful website. I assumed everyone should have a modern browser nowadays, I was wrong! with a look at my visitors stats I noticed I have many visitors with very old browsers, and needless to say, none of them could see my cool CSS and HTML5 designs...
IMO, you should first focus on making your content available to everyone, don't forget there are many users who never install any third-party browser and sometimes they even forget to update the browser that came with their OS.
This is a controversial subject: Backwards Compatibility v Progressive Enhancement. If you land somewhere in the middle, you'll do fine.
