There are too many browser versions, which is also tiring, especially those of the IE family.
I searched a lot on the Internet and found that what was said was different from what I saw. It turned out that there was a problem with the other party's expression, and there was an ambiguity due to the omission of a few words.
According to what is said on the Internet, the box model interpretation of ie6 does not comply with the W3C standard. In fact, it should be The box model interpretation of ie6 in quirks mode does not comply with the W3C default standard, while ie6 in standard mode The interpretation of the box model in mode complies with the W3C default standard.
This involves how to trigger the working mode of ie, which is mainly defined through doctype. You can see it clearly in the screenshot below:
(Q: Quirks Mode, weird mode; S: Standards Mode, standard mode; A: Almost Standards Mode, almost standard mode)
Interested friends can go to this website (English): https://hsivonen.fi/doctype/
Here is a friendly reminder: bootstrap V3 is correct Some elements (especially elements related to layout) are set with box-sizing:border-box, which means that the box model is parsed according to IE's weird mode, because this parsing is very friendly to layout! Unfortunately box-sizing does not support ie6, only ie8 supports it, so if you want to be compatible with ie6, be careful. Because the parsing of the box model in IE6 in standard mode complies with W3C standards, but bootstrap V3 requires the parsing of the box model in IE's weird mode!