Need help identifying component

[SilverMarcs]

Hi. How can I color only this part as highlighted in red. Need to keep all other colors constant. What is the name of this section? Got no experience, was just modifying another preexisting themes so detailed instructions would be appreciated. Thank you

[mjabdulm]

toolbar-ThreadList ( if the section is above thread list)
or
toolbar-RootSidebar ( if the section is above the account/folder bar)

TO get the component name:
You can type:

1. +I to opent the web inspector.
2. Then, click the top-left most icon of the web inspector,
3. Now point the mouse cursor on the component to find the name of it.
   Hope this helps.