Valmiki Ramayana Yuddha Kanda Sarga 4 Shloka 118

सागरम् the ocean, अम्बरप्रख्यम् resembling the sky, अम्बरम् sky, सागरोपमम् like the ocean, सागरं च and the ocean, अम्बरं चेति like the sky identical, निर्विशेषम् not at all, अदृश्यत not appeared

The ocean resembled the sky and the sky like the ocean were identical as no difference appeared.