“Vous etes la plus belle de toutes” and a little rose… What a romantic text on this delightful gold button.
“As cute as a button”, means “cute, charming, attractive, almost always with the connotation of being small.
How cute can a button be? The key to the issue is that it is not the button on a shirt that is meant here, but a flower bud in the popular name of a small flower. Indeed, cute as a flower bud.
The phrase is only used for small objects, animals, people – you’d say that a child, or maybe a small dog, was as bright as a button, but you’d never say it of a six-foot man. So the image is of a little sparky thing.
The British version can also be “bright as a button”, which may be the original one since it alliterates. “Bright” makes sense if you think of a polished metal button. Since at least the 15th century, the adjective “bright” has been used to describe the beauty of a flowering bud, so the phrase “bright as a button” can still initially refer to a flower bud.