CSS Logical Properties

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A property like margin-left seems fairly logical, but as Manuel Rego Casasnovas says:

Imagine that you have some right-to-left (RTL) content on your website your left might be probably the physical right, so if you are usually setting margin-left: 100px for some elements, you might want to replace that with margin-right: 100px.

Direction, writing mode, and even flexbox all have the power to flip things around and make properties less logical and more difficult to maintain than you'd hope. Now we'll have margin-inline-start for that. The full list is:

  • margin-{block,inline}-{start,end}
  • padding-{block,inline}-{start,end}
  • border-{block,inline}-{start,end}-{width,style,color}

Manuel gets into all the browser support details.

Rachel Andrew also explains the logic:

... these values have moved away from the underlying assumption that content on the web maps to the physical dimensions of the screen, with the first word of a sentence being top left of the box it is in. The order of lines in grid-area makes complete sense if you had never encountered the existing way that we set these values in a shorthand.

Here's the logical properties and how they map to existing properties in a default left to right nothing-else-happening sort of way.

Property Logical Property
margin-top margin-block-start
margin-left margin-inline-start
margin-right margin-inline-end
margin-bottom margin-block-end
Property Logical Property
padding-top padding-block-start
padding-left padding-inline-start
padding-right padding-inline-end
padding-bottom padding-block-end
Property Logical Property
border-top{-size|style|color} border-block-start{-size|style|color}
border-left{-size|style|color} border-inline-start{-size|style|color}
border-right{-size|style|color} border-inline-end{-size|style|color}
border-bottom{-size|style|color} border-block-end{-size|style|color}
Property Logical Property
top inset-block-start
left inset-inline-start
right inset-inline-end
bottom inset-block-end