Works of art with a beautiful/idyllic aesthetic might use harmonious colors, balanced compositions, organic shapes, perhaps flowing lines/brushstrokes. If representational, the works might depict characters or scenes that are naturally appealing, at ease, and in full-health/full bloom.
An artist might manifest a beautiful aesthetic in a piece due to his or her own personality, or the artist might choose this aesthetic as a reflection of the characters/objects/moment in history being portrayed. A beautiful aesthetic might also be adopted to make a piece suitable for a setting or purpose that demands something beautiful.
Featured: The Kiss by Gustav Klimt.