If i can understand your point is, Front end as in HTML, Bootstrap , CSS and Jquery(if). Your company is having web application design from some other party and you need to write the logic and database.
1. How to decide front-end design is good?
Ans: That depend upon your web application requirements. If design is what you are looking for. You can see if coding standards are properly followed, CSS and Jquery (if any) files are reusable and/or placed in a common location. No redundant code.Later you might need to change HTML tags to server side tags(if needed) so that flexibility is there or not
2. Which type of question should I ask to them?
Ans: This is depend upon your capability by seeing the requirement document and getting understanding about web application.
3.IS THERE ANY SPECIFICATION OR RULES WHICH IT INDUSTRY FOLLOWS WHEN THEY MERGE FRONT-END AND BACK-END?
Ans: Rules are not specific. It varies from one to another. guidelines are there on internet you can read. Main thing is re-usability and coding standards.
4. what care should I took in this case?
Ans: go to
http://www.asp.net/[
^]
if you very new to web application development.