Re: Which browser are you using?
I think IE and Opera were released to the public at more or less the same time. IE was 1995 and Opera 1996. I'm not sure either were used too much back then because Netscape was a popular browser.
Opera used the 'Presto' engine for years but now uses 'Blink' the same one as Chrome.
Ages ago, when I put my web site together, I had to make sure it looked the same in Opera (Presto engine) Netscape (Gecko engine) and Internet Explorer (Trident engine) because they all interpreted HTML code slightly differently.