CSS Logical Properties and Values provides a writing mode-based layout method, using inline, block, start, end and other logical directions to replace the traditional left, right, top, and bottom. 1. It enables the style to automatically adapt to LTR, RTL and vertical layout without additional adjustments; 2. Common properties include margin-inline-start, padding-block-end, inline-size and block-size; 3. Applicable to international websites, component library development and responsive design; 4. Be careful about compatibility when using it, and some browsers may need fallback processing.
CSS Logical Properties and Values is a CSS feature that defines layout and style based on writing mode. Instead of using left, right, top, bottom like traditional physical properties, they use more abstract logical directions, such as inline, block, start, and end to describe the position and dimensions of elements.

The advantage of this is that whether your content is left to right (LTR), right to left (RTL), or vertical arrangement (such as Chinese vertical text or Japanese layout), the style can be adapted automatically without additional adjustments.
Why are logical attributes needed?
In traditional CSS, we are accustomed to using physical direction properties such as margin-left and padding-right. However, when faced with different text directions or page layouts, these attributes appear to be inflexible enough. For example:

- In RTL mode, the meanings of left and right are reversed.
- In vertical layout, top and bottom may no longer be "up and down", but "front and back".
Logical attributes introduce the concepts of inline (inline direction) and block (block level direction) to make the layout more in line with the writing logic of the content.
For example:

-
margin-inline-start
indicates the margin on the side where the content starts in the inline direction.- LTR is equivalent to
margin-left
- RTL is equivalent to
margin-right
- Under vertical layout, it may correspond to the top
- LTR is equivalent to
What are the common logical properties?
Here are some commonly used logical properties and values, as well as their corresponding physical properties (depending on writing-mode and direction):
-
Box model related
-
margin-inline
,margin-block
-
padding-inline
,padding-block
-
border-inline-start
,border-block-end
-
-
Dimension control
-
inline-size
: Controls the size of the inside direction (replaces width) -
block-size
: Controls the size of the block-level direction (replaces height)
-
-
Alignment
-
text-align: start | end
: more general than left/right -
justify-content: flex-start | flex-end
also gradually supports logical values such asflex-inline-start
(some browsers have already supported it)
-
Actual usage scenarios and suggestions
-
International website or multilingual project
- If you are developing a website that supports RTL or Chinese, Japanese and Korean vertical text, logical properties can reduce a lot of redundant style coverage code.
-
Component library development
- Components should be as free as possible to rely on specific writing directions. Using logical properties can make components more adaptable.
-
Dynamic direction switching in responsive design
- The page may dynamically switch direction according to the user's settings (such as switching LTR/RTL through buttons), and the logical properties can automatically adapt to this change.
?? Pay attention to compatibility: Currently, mainstream browsers have supported most logical properties, but if you still need to be compatible with old browsers (such as IE), you may need to use fallback writing or use PostCSS plug-in for downgrade processing.
Tips: How to quickly determine which logical attribute should be used?
- Want to express "left" or "right"? Change to
*-inline-start
or*-inline-end
- Want to express "top" or "bottom"? Change to
*-block-start
or*-block-end
- Want to express width or height? Switch to
inline-size
orblock-size
Basically that's it. Logical attributes are not necessary, but they are very practical in multilingual or multi-typed scenarios, and are worth understanding and trying in advance.
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