Unwanted change of MenuFont in Main theme after adding to cart

-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7.2
-- PHP version -- : 7.1.5

At the moment I am building and testing a website and I encounter a weird problem.
Let's see if I can explain what happens:

After adding a product to my cart and continue the checkout, the font of MenuTabs in my Theme changes (see attachments).
Of course I don't want my original thema to change.
I have another website (same theme, same setting) where this problem doesn't occure.


I can't figure out why this happens and how to fix this.
What can I do?

EDIT:
I just noticed that the error doesn't occure when I disable "Display checkout progress bar" ...
(But I like it better with the progressbar ...)

Hello,

It looks more than weird that the cart content will affect the font of your menu.
You gave a private link but it is not possible to access the website ; so unfortunately, we are not able to take a look. Which mean that we can't provide you any further detail.

All I can tell you right now is that you need to analysis the CSS rules to understand what is going on :
www.hikashop.com/support/documentation/1...the-display.html#css

Regards,

It's even weirder: The problem solved itself!

I set "Display checkout progress bar" to "No checkout progress". After I did this the problem didn't occure anymore.
When I returned to the first setting "Checkout progress with ending" the Menu-Font didn't change anymore.
No idea why, but I am glad it works now.

I found out that the problem occured when I use https
Fonts are being blocked on https. When I disable https in my site, the fonts are loaded without any problem.