I have a current website dating back to the good old table days. I am in the midst of changing the website to be responsive with style sheets etc etc.
My index page in the current website is .HTML but all other pages are .HTM and in order not to affect my rankings I intended to save the new website in the same way.
When I looked at my new index page in Opera it displays perfectly but the other pages saved .HTM appear significantly different especially text sizes and buttons. I am going out of my mind trying to fathom out why saving a file .HTM rather than .HTML should make a blind bit of difference to the website appearance.