css grid, css flexbox, bootstrap

Hi there myself Nyay D.G. while making this web page I learned various things and it just seems like I made a out line and then adjusted things as per necessary. I used bootstrap,css grid and also css flexbox.Mostly I used flexbox and grid and there is practically no use for bootstrap but there I added it because if I decided to increase the functionality of page in future it will be helpful. I am just beginner so help me in any way possible and tell me the way to improve it.