[TMCU-985] Update Toast in extension

### Description\n\nMirrors Jira [TMCU-985](https://consensyssoftware.atlassian.net/browse/TMCU-985).\n\nPart of epic #1271 / [TMCU-622](https://consensyssoftware.atlassian.net/browse/TMCU-622).\n\n**Jira 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_](https://consensys.slack.com/archives/C02VD8QG0LT/p1783009607167229?thread_ts=1782997745.906819&cid=C02VD8QG0LT)_._\n