"Current" state not honored when site is exported

For the main navigation of my site, I have the text decoration of the “current” state of the links set to underline. This works when publishing the site to Webflow’s servers, but not when exporting the code and uploading it to the servers of my web host, Siteground.

I made a 1:37 video that demonstrates the issue:

Any advice anyone could offer would be appreciated.


Here is my site Read-Only: http://bit.ly/2ZG3JpR