As @felgall said:
You should use one or the other for the text on your page and not try to mix them or your page will break.
em is intended for defining text size.
px is intended for defining border widths and image sizes.
Now i use em for text size and px for others. But i still confusing when using both em and px in my design. Example
Is above code ok? Hope everyone give me advice. Thank in advance.