The boxes width are now controlled through a Php variable on line 14 of product_attributes.php, set the number of pixels you desire, the boxes will automatically fit the size. Thanks to user andyisgreat who made me notice that users may want to change their boxes' size depending on their needs.
Furthermore, an important correction was made: the page navigator doesn't forget the active tab any more, it used to when more than 10 elements were displayed. Thanks to user mwildin1 for finding this one.

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