I have been studying block chain for a while, and I came to know that decentralisation of data is its greatest pros. From my understanding, if block chain is massively adopted in the future, we will no longer need servers, since everything will be stored on the block chain. Currently, we can store solidity smart contracts on the block chain. However, we still need a server to store HTML, CSS, and many other scripts. So, my question is, how is block chain beneficial when we still need a server to run applications conveniently? Where is the decentralisation here?
Blockchains won't most likely ever replace stuff like regular servers. Blockchains are deterministic and they are not suited for stuff like hosting websites.
The decentralization of blockchain is about the data they contain. So if you upload a smart contract which for example calculates numbers together everyone can access the same contract and it's not stored in any centralized server - it's stored in all nodes which implement the blockchain. Currently for Ethereum there are a bit less than 10000 nodes which makes the blockchain quite decentralized.
So only part of the stuff which are hosted in centralized servers currently can be put into blockchain. The idea is that you keep some important logic/data in blockchain and everyone can create their own user interface to access that data. For example the various decentralized finance contracts which already exist in the blockchain - they just provide the platform and everyone is free to create their own user interface to utilize the functionality.