Beauty of contours seen in sweethearts (10)

I believe the answer is:

loveliness

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'beauty' is the definition.
(I know that loveliness is a type of beauty)

'contours seen in sweethearts' is the wordplay.
'contours' becomes 'lines' (I can't explain this - if you can you should believe this answer much more).
'seen in' means one lot of letters goes inside another.
'sweethearts' becomes 'loves' (I've seen this in another clue).
'lines' put within 'loves' is 'LOVELINESS'.

'of' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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