Tweak avi follow button styles (#4304)

* Tighten up

* Tweak colors

* Tweak for night mode

* Add missing file

* Contrast plus

src/alf/util/themeSelector.ts

@@ -0,0 +1,14 @@
+import {ThemeName} from '#/alf/themes'
+
+export function select<T>(name: ThemeName, options: Record<ThemeName, T>) {
+  switch (name) {
+    case 'light':
+      return options.light
+    case 'dark':
+      return options.dark || options.dim
+    case 'dim':
+      return options.dim || options.dark
+    default:
+      throw new Error(`select(theme, options) received unknown theme ${name}`)
+  }
+}