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CSS logical properties describe layout relative to an element’s writing flow, so margin-inline-start means a margin at the start of the text line—on the left in horizontal LTR and on the right in horizontal RTL. Use them when spacing, sizing, or placement should adapt to writing direction or mode; keep physical properties when a design is intentionally tied to a fixed screen edge.
What are CSS logical properties?
Physical CSS properties name fixed edges or dimensions: left, top, width, and height. Logical properties name positions and dimensions in relation to the content flow: inline-start, inline-end, block-start, block-end, inline-size, and block-size.
The inline axis runs along a line of text; the block axis runs perpendicular to it, in the direction blocks progress. MDN summarizes the distinction as the inline dimension being parallel to text flow and the block dimension perpendicular to it. Neither axis is inherently horizontal or vertical. MDN’s basic concepts guide explains the model.
How do CSS logical properties work with RTL and vertical writing?
The mapping depends on the element’s writing context, shaped by writing-mode, direction, and text-orientation. In broad terms, direction sets the inline base direction, writing-mode sets block-flow direction, and text-orientation affects glyph orientation. Logical properties are therefore not simple aliases for “left” or “top.” See the W3C CSS Writing Modes specification.
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| Flow-relative intent | Horizontal LTR | Horizontal RTL | Vertical writing |
|---|---|---|---|
| Inline start | Left | Right | At the start of the vertical text line; margin-inline-start can map to top |
| Block start | Top | Top | At the start of block progression, on a horizontal side |
| Inline size | Extent along the horizontal text line | Extent along the horizontal text line | Extent along the vertical text line |
| Block size | Extent perpendicular to the text line | Extent perpendicular to the text line | Extent perpendicular to the vertical text line |
In a vertical writing mode, the inline axis becomes vertical and the block axis horizontal. MDN documents margin-inline-start mapping to margin-top in a vertical mode; use the axes rather than memorizing one physical side. MDN’s margins, borders, and padding guide provides usage details.
How do I replace margin-left with a logical property?
First decide what the margin means. If it belongs at the start of the reading line and should flip in RTL, use margin-inline-start. If it must remain on the physical left regardless of writing context, retain margin-left.
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/* Flow-relative: follows the start of the text line. */
.item {
margin-inline-start: 1rem;
}
/* Physically fixed: always on the left. */
.stuck-to-left-edge {
margin-left: 1rem;
}A broad search-and-replace of every left with inline-start is unsafe: first establish whether the design is flow-relative or physically anchored.
Which properties have logical equivalents?
Logical properties cover more than margin and padding. Common families include sizing, borders, insets, and flow-relative values for float, clear, and alignment. The MDN logical properties guide documents the broader set.
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| Intent | Physical example | Flow-relative option |
|---|---|---|
| Dimension along the text line | width |
inline-size |
| Dimension perpendicular to the text line | height |
block-size |
| Margin or padding at inline sides | margin-left, padding-right |
margin-inline-start, padding-inline-end |
| Border at inline start | border-left |
border-inline-start |
| Position at a flow-relative edge | top, left |
inset-block-start, inset-inline-start |
| Alignment relative to flow | left or right alignment |
start or end alignment values where supported by the property |
Logical mappings also exist for border radii, float, and clear. Choose the flow-relative form only when the intended relationship is to the writing context.
What is the difference between inline-size and width?
width always describes the physical horizontal dimension. height describes the physical vertical dimension. inline-size describes size along the inline axis, and block-size along the block axis. In horizontal writing, inline-size is usually horizontal; in vertical writing, it is vertical. If a component should retain its sizing relationship to text flow across writing modes, logical sizing expresses that intent.
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Build a component with logical spacing and borders
.card {
inline-size: min(100%, 42rem);
padding-block: 1rem;
padding-inline: 1.25rem;
margin-inline: auto;
border-inline-start: 0.25rem solid currentColor;
}Here the card’s extent follows the inline axis, padding is specified along both axes, and its border is at inline-start. In horizontal LTR the border is on the left; in horizontal RTL it moves to the right. These declarations express intent rather than promising any particular physical orientation in every writing mode.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use logical properties for positioned elements when placement follows flow
For an element whose position should track the writing context, use inset-block-start, inset-block-end, inset-inline-start, or inset-inline-end. Keep top, right, bottom, and left when placement is deliberately attached to fixed physical edges, such as a viewport corner.
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Do logical properties change four-value shorthands?
No. Four-value shorthands such as margin, padding, and border retain their physical meaning. For example, margin: 1px 2px 3px 4px means top, right, bottom, and left—not block-start, inline-end, block-end, and inline-start. Use logical longhands or axis shorthands such as margin-inline when the sides should follow flow. The MDN guide covers the logical spacing properties.
What happens when physical and logical declarations are mixed?
Corresponding physical and logical properties participate together in the cascade according to the element’s computed writing mode; they are not wholly independent groups. This can make an apparently unrelated change to direction affect which physical side corresponds to a logical declaration. The W3C CSS Logical Properties and Values Level 1 Working Draft, dated 4 December 2025, demonstrates this behavior. A Working Draft is not a final Recommendation.
- Prefer one clear property model for a component instead of layering physical and logical declarations without a reason.
- If you need a fallback or override, check declaration order and the element’s computed writing mode, not just the visual result in one LTR layout.
- Use semantic document markup and appropriate direction settings for bidirectional text; logical properties alone do not solve text ordering.
Do CSS logical properties work in vertical writing modes?
They are designed to express relationships to the writing axes, including vertical writing. Check the intended writing mode and the relevant property mapping rather than assuming that inline means horizontal or block means vertical. MDN’s guides describe the behavior, but the material cited here does not establish a browser-version support matrix; consult a current compatibility reference before setting a specific minimum-browser requirement.
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Quick Recap
How to choose between physical and logical CSS
- Use logical properties when the design intent follows the text line or block progression, or the component needs to adapt to RTL or vertical writing.
- Use physical properties when a size or edge is intentionally tied to the horizontal/vertical viewport or another fixed physical reference.
- Review shorthand and cascade behavior whenever physical and logical declarations coexist.
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