[TMCU-986] Update Toast in mobile

### Description\n\nMirrors Jira [TMCU-986](https://consensyssoftware.atlassian.net/browse/TMCU-986).\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 a mobile 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 mobile.\n\n_Work item created in Slack from a_ [_message_](https://consensys.slack.com/archives/C02VD8QG0LT/p1783009607167229?thread_ts=1782997745.906819&cid=C02VD8QG0LT)_._\n