EM in CSS different size on wordpress then elsewhere [closed]

From the spec:
“EM is Equal to the computed value of the ‘font-size’ property of the element on which it is used.”

You have a different font-size value between the two URLs you provided (14px and 10px respectively).

Line 273 of your style.css file is replacing the default Bootstrap font-size for the body element (line 5 of bootstrap.min.css).