Set the space between direct siblings

.flow > * + * {
  margin-block-start: var(--flow-space, 1em);
}

My favourite 3 lines of CSS by Andy Bell is not only three lines of code to set the space between direct siblings that works for any block flow direction. Andy explains why he is using custom properties and how to tune the setting for different contexts, like in prose text and spacing around the figure element or headings.

The Stack as a further resource is excellent. It´s adding the idea of modular scale.

It´s worth reading Andy´s 24 Ways article Managing Flow and Rhythm with CSS Custom Properties. The text does not use CSS logical properties, because it is dating back to 2018, but is a good companion resource.