Adobe XD Dimensions NOT Accurate

I've noticed that what is shown in preview of desktop after forming vector images, text, layout dimensions, etc., is NOT the same after exporting the images & setting the same dimensions in code. In other words, when I try to set the same width or font size as shown in Adobe XD dimensions, it is MUCH larger after setting the same in my CSS & I have to create my own dimensions to make everything look balanced. Why doesnt XD have accuracy with real code dimensions?