Please share Karl Marx's contribution, that made the current day better than before..

I will start with one.

Marx’s theory of value, perhaps his most important contribution to the field of economics, albeit, the most rejected — stated that the value of any given commodity is determined by the socially average simple labour time used to create it, giving skilled labour value in multiple units of unskilled labour, suggesting that the market determines all prices based on this mythical underlying labour cost.