Why my website looks different on computer?

Why my website looks different on computer? on my localhost it looks like this: https://imgur.com/a/5k4GRXl and when i upload my files on host website and check my website it looks like this: https://imgur.com/a/YQyHWjo I’m using HTML5,CSS3 and Bootstrap 4, anyone know how to solve it?, i used css3 only for the size of carousel thing, padding at navbar and at the HR tag, first i thought the host don’t recognize the css file but why my ABOUT ME button is not on the right position i used only bootstrap classes for button, Sorry for my bad english, hope you answer to my question. P.S: On mobile or tablet looks very good, but on pc it looks like in the image.