Valmiki Ramayana Kishkindha Kanda Sarga 58 Shloka 17

असिते in dark, राक्षसे on the demon, तस्याः her, उत्तमम् fine, कौशेयम् silken cloth, शैलाग्रे on the peak of the mountain, सूर्यप्रभेव like the radiance of Sun, अम्बुदे in the dark cloud, यथा like that, वा तटित् यथा like lightning, भाति shining.

'Her fine silk garment was shining like the radiance of the Sun on the mountain peak, like lightning against the dark cloud. (That was Ravana).