would it be possible to remove the color of container line for above each tab

[Parthvsquare]

The current setup

This is how safari looks like

Using on catalina .15.7

[Chris111212]

or do a colored dot for each container?

[AdamXweb]

It's definitely possible, however may come down to user preference.
Seeing as on Firefox, the multi tab container is a feature Safari doesn't have I'd argue that colour of some kind should be there.
You can add the following code into your customChrome.css (if you don't have one, make one in the same chrome folder.

.tabbrowser-tab[usercontextid] > .tab-stack > .tab-background { border-top: 3px solid transparent !important; }

[AdamXweb]

Also for reference, these are the standard identity colour locations that Firefox supports.

Could always have some kind of vote, or a script that can change the location as it may come down to user preference.

[Parthvsquare]

Thanks man,
.tabbrowser-tab[usercontextid] > .tab-stack > .tab-background { border-top: 3px solid transparent !important; }
this added a separation so i removed the 3px