Apparantly IE11 doesn't have a User Agent Style for <main> and therefor no display: block; on it. Why is there no User Agent Style? Is this a bug or on purpose?
Adding display: block; to the main element is enough, tho.
The main element is indeed not fully supported by IE11. Adding main { display: block; } to your CSS is the best solution for IE9+. You don't need to make conditional comments - since display: block; is the default behavior for main elements, it won't mess up anything.
来源：https://stackoverflow.com/questions/20094276/ie11-is-missing-user-agent-style-for-main-element-display-block