Push and Pull move the columns visually e.g. we use position relative and then we apply left or right offset. The column stays in the same place, but is just visually offset.
Offset on the other hand uses margin e.g. "physical" offset and pushes the following columns.
Put in other words, if you have two columns each 2 units wide:
1) if you apply push 2 on the first it will be above (or below) the second column
2) if you apply offset 2, the first column will move 2 units to the right, but will also move the second column
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