The darkened areas over the ankles and elbows are likely due to post-inflammatory hyperpigmentation or frictional melanosis, commonly aggravated by constant pressure, dryness, and inadequate moisturization. In some cases, acanthosis nigricans can also present similarly.
Next Steps
For effective lightening, I recommend an online consultation with a dermatologist to assess your skin type and guide you on safe topical depigmenting agents like glycolic acid, lactic acid, or urea-based creams which work better than home remedies.
Health Tips
Avoid harsh scrubbing or overuse of lemon/besan packs as they can irritate and worsen pigmentation. Regular use of a urea-based moisturizer and gentle exfoliation under supervision can gradually improve skin tone.