Support out-of-month days style

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Summary

Feature suggestion: Style out-of-month days in flowbite-react Datepicker

Out-of-month days (the leading/trailing days from the previous/next month shown to fill the month grid) currently render with the same visual emphasis as in-month days in the flowbite-react Datepicker. This makes the calendar harder to scan and reduces parity with Flowbite’s HTML datepicker styling.

Desired behavior

When the Datepicker renders a given month view (e.g., “January 2026”), any day cell that belongs to December 2025 or February 2026—but is displayed in the January grid—should be visually de-emphasized.

Proposed default behavior:

• Apply reduced opacity (e.g., opacity-40) and/or muted text styling (e.g., text-gray-500) to out-of-month day cells.
• Keep out-of-month days interactive (clickable) unless they are disabled by min/max date constraints.
• Ensure selected styling overrides out-of-month styling so selection remains clearly visible.

Suggested API improvement

Add a theme token for out-of-month days

Extend the existing theme structure with an outside (or outOfMonth) style key for day items:

views: {
  days: {
    items: {
      item: {
        base: "...",
        selected: "...",
        disabled: "...",
        outside: "opacity-40 text-gray-500", // custom style
      },
    },
  },
}

Current Behaviour

Expected Behaviour

Context

Why this matters

• Improved readability: Users can immediately distinguish which days belong to the current month vs. adjacent months.
• Better ecosystem consistency: Aligns the flowbite-react Datepicker with the visual semantics users expect from Flowbite’s datepicker patterns.
• Avoids brittle workarounds: Without a supported hook, consumers resort to DOM querying / MutationObservers to post-process day elements, which is fragile against internal markup changes.