Set absolute path for root directory in HTML on local filesystem

How can I use absolute paths in my website while testing on my local filesystem? I know that I can use / to access the root directory of my website. However, this works only when my website is on the server. I want to be able to use absolute paths on my local filesystem so that I can do proper testing before uploading.

Is there a way to set a variable to a root directory in HTML? Something similar to Linux where you can define a variable WEBPATH=/home/user/website. Thus I can use e.g src="WEBPATH/folder/file.html for all the files I use in my website and I can modify WEBPATH depending on whether I am testing locally or using the server root folder.

I am open to other workarounds as well.