Unit size expressions are “% of viewport width”.

Size 50 = 50% of viewport width (in any aspect ratio), even when used in a height property.

Flex settings apply to the children of the object, unless these children have absolute positioning.

Absolute positioning will ignore the parents flex settings, but still anchor it relative to its parent.

Padding is adding space inside the bounding box of an object.

Margin is adding space outside the bounding box of an object.

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