This is pretty much my breakdown (and actually Marx's as well I think, the guy's mistaken there). America is weird because they try to create classes out of income streams but no one else does that. Classes are groups of people who live different lives, with different strategies and worldviews not someone earning a few dollars more than someone else.

The working class is anyone who has to sell their labour to survive. This is the vast majority, 85-95% of the population depending on where you live. You can be rich and still working class if you rely on someone else employing you in a salaried position. The point is your ability to earn is in the hands of others so you have to learn to fit in to someone else's way of working and you have no control if the company goes under. However this is still a relatively stable and low risk way to live. There isn't really a political movement which caters to this group solely which is why most countries have a near 50/50 split left and right. The closest would probably be democratic socialism. Socialism does really appeal to most working class people because they don't want to be responsible for owning the means of production, they just want to do their job and let someone else worry about that.

The middle classes are the business owners, inventors, traders, entrepreneurs, etc. They can make money out of things they own including their own ideas. They still have to work hard but because they see direct rewards for all the work they put in they enjoy it, the middle class work ethic. They have a different idea of risk and guilt because they generally won't fund their enterprises themselves so operate through loans and usually have multiple failures over their careers which they have to get over and start up again (causing working class people a lot of pain in the process). The middle class professions are the ones which lead eventually to owning a business if you're good enough, law, medicine, accountancy, etc which is why university education mistakenly gets associated with this class. Before the enlightenment the middle classes were oppressed and despised pretty much everywhere (seen as taking a cut out of other's labour without adding anything) which is why they are so pro individualism and human rights even now. Liberalism was/is their political ideals which benefit them particularly and makes them rich. While traditionally speaking these people are middle class some of the richest people in the world now belongs to this class because of the liberalisation of the markets and business. Someone like Warren Buffett still goes to work everyday, fiddles with his investments everyday, even though he doesn't have to. The mindset you have can very much keep you from moving up in class.

Then you have the upper class. These are people who are so wealthy they never have to work. They don't even have to manage their money or property, they can pay someone else to do that for them. However their fortunes are at the whim of long term social change which is why they are politically conservative. When the enlightenment came in many of the old rich families lost their fortunes as land lost its value. The smarter families simply married into the richest middle class ones every couple of generations. The richest middle class move into this bracket when they have their money in more than just their own business so are no longer relying on their own brains and labour. The current method is to put millions into charities so you can claim wages and expenses through them and avoid tax but more importantly use that charity money to create massive social influence. Warren Buffett has set all his kids up with massively funded charities so while he is still a hard working middle class guy his kids be upper class.