The exported csv of customer's is the representation of current customers on your website. That csv is not intended to be used to import customers. For that you need to create a csv similar to sample customer csv in import panel (https://prnt.sc/uhgq84).
The exported csv does not contain the password field for security purposes, to prevent password from being stolen.
The password is blank when editing customer for the same reason.
The css of black black background is written in the header file itself.
You have to open /themes/hotel-reservation-theme/header.tpl and at line 87 change the background-color code as per your desire. (Current color code is #252525)
Well, all the blocks on the home page of the current theme are dynamic. You can modify the content you upload to show any kind of information you want.
But if you want to develop a new block on the front then right now we do not provide the technical assistance for development.
But soon we will launch our dev docs for such kind of help.
Until then you can follow Prestashop dev docs as QloApps is built on Prestashop.