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okey! the package boiboites found as a file attachement in https://www.alexisfles.ch/en/latex/boites1.html

Thank you so much for your answer! I have already used the tcolorbox package but I always get errors because of this package!!!!!!

Good morning
I want boxed-theorem such that theorems must be enumerated by sections, I found this code,I and I tried to do changes in order to enumerate theorems by sections but it didn't work!
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath ...