Add subtle background color difference to read and unread emails in /e/ Mail on Select

Summary

Add subtle background color difference to read and unread emails in /e/ Mail on Select. Currently there

This improvement concerns

What is the current behavior?

Currently, there is no visual difference between the read and unread mail, when selected.

Also, no visual change is made, when selected email changes read/unread status.

What is the improved behavior?

Read and unread status should be visible, when emails are selected.

What does it bring?

Better user experience, when the user wants to do action only on the few unread or read and read or unread emails are in the list, too.

Visual change when the user changes read/unread status on the selected items.

Select unread mails, mark as read and see a visual change.

Select unread and read mails and still be able to differentiate visually between a read and unread email.