The Variables tab lets you easily define & change variables on your site and override some variables like the ones listed here.

The Styles tab provides access to the settings you defined in the Variables tab, and it lets you make other custom changes.

Last but not least, we have the Scripts section of your theme editor. This is where you can add custom JavaScript to your Streamline site.

Click "Save scripts" and this will save all changes made in all 3 tabs.

Make sure you see the "All changed have been saved!" banner.

Streamline Advanced Theme Editor