You can edit Cart Page Header Style by following these steps:
#1. First, you enable the Cart Icon in the Site Header
We do this, to be able to access the Cart Page in Edit Mode more easily, you can disable it later if you want.
#2. Next, click the Cart icon, it will open the Cart Page.
Click the Site Styles icon.
#3. Choose Fonts or Colors
#3.1. If you choose Fonts > Next, click on Header on the Left side >> SS will open some options, you can adjust header size here. (Note: This will affect all pages)
#3.2. If you choose Colors, click Edit in LIGHTEST1
Next, hover on the Header (left side), you will see a blue border around the header > Click on the Header
The right side will open the exact options. You can change it here, it will affect the Cart Page Style. (Note: All sections, use LIGHTEST1 on other pages, will also be affected)