Add more themes and rustfmt

assets/themes/gruvbox-darkest.toml

@@ -0,0 +1,23 @@
+name = "gruvbox-darkest"
+
+[colors]
+bg = "#121212"
+fg = "#ebdbb2"
+text_correct = "#b8bb26"
+text_incorrect = "#fb4934"
+text_incorrect_bg = "#462726"
+text_pending = "#a89984"
+text_cursor_bg = "#fabd2f"
+text_cursor_fg = "#121212"
+focused_key = "#fabd2f"
+accent = "#83a598"
+accent_dim = "#3c3836"
+border = "#504945"
+border_focused = "#83a598"
+header_bg = "#3c3836"
+header_fg = "#ebdbb2"
+bar_filled = "#83a598"
+bar_empty = "#3c3836"
+error = "#fb4934"
+warning = "#fabd2f"
+success = "#b8bb26"