beautiful as a jewel
瑶 centers on the beauty and preciousness of fine jade or a jewel. The given meaning 'beautiful as a jewel' is a single conceptual image of gem-like beauty.
瑶 combines 王 (jade) with 䍃, which likely contributes the sound and may relate to a precious stone or ornament. The exact historical development of 䍃 is uncertain.
The left side 王 (jade) tells you this is about a precious stone. The right side 䍃 looks like a container holding something valuable. Together they suggest a jewel as beautiful as fine jade.
For ヨウ, imagine a beautiful jewel glowing with a soft yo~u can see: yo~u -> ヨウ, and the jewel's beauty draws you in.