How do I change the size of admin dashboard widgets ?

Hello,

For some reason, my admin dashboard widgets are displayed in a weird way. They are displayed on two columns (which I want to be so), BUT the two column don't have the same size (see file A attached).

On the previous version of my site, the display on 2 columns is correct (see file B attached).

Please note that the widget called "Créer son ePortfolio - Guide de démarrage" is made with your Custom Dashboard Widget plugin.

How should I correct that display problem so the two columns are even ? Using CSS ?

Please let me know, thanks a lot for your help !

DJ