How to get blocks with same heigh in columns?

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Finally, I found a solution with flex attributes:

I defined the following CSS rules :

.flexColumn {
    display: flex;
    flex-direction: column;
    align-self: auto !important;
}

.flexItem {
    flex-grow: 1 !important;
}

I can now apply flexColumn to the columns and flexItem to the items that I want to grow to fill the empty space:

enter image description here

For some items I also need to deal with top/bottom margins (margin-top:0)