I am designing a website using bootstrap ,HTML,CSS,CSS3 and PHP as Server side language. But when i checked it on different Browser I found that it is not compatible for all browser by examining some appearance and functionality of HTML elements. I want my web page should look on every browser.

I wanted to know : 

1) What are the aspects that we have to take in consideration while designing cross-browsing website?

2) How can i design a page which can give me the same output on different browser.