[TMCU-985] Update Toast in extension

[georgewrmarshall]

Description\n\nMirrors Jira TMCU-985.\n\nPart of epic #1271 / TMCU-622.\n\nJira status: In Progress\n\n### Jira details\n\n### User story\n\nAs an extension user, I want the Toast component to be updated to match the pure black background schema.\n\n### Context\n\nPart of the pure black background schema update.\n\n### Acceptance criteria\n\n* Toast component background updated for extension.\n\n_Work item created in Slack from a_ message.\n