The classical middle class, c. 1850, was quite affluent, maybe professionals (doctors, lawyers) and with substantial wealth. Some property (but not too much). Quite independent. We would now call that lower upper or even middle upper, although doctors are being down-classed.
After WWII, say 1955, it became a home with mortgage, a car with loan, a TV, struggling to put one kid through college.
Now in Seattle or Portland, it is an iPhone, a morning latte and a nose ring.
And upward social mobility in Seattle means living in your car when you work at Amazon.com because you can’t afford an apartment.