block-size
Defines the 'height' of an element in a way that respects the writing mode. If you switch from horizontal to vertical text, 'block-size' automatically switches from height to width so your layout remains consistent.
Quick example
.modern-container {
/* Respects writing-mode: usually height in English */
block-size: 300px;
background: #f1f5f9;
}Quick facts
Initial value
autoInherited
No
Applies to
same as width and height
Animation type
lpc
Values
width block-size Browser Support
Widely available Since 2021 95% global usage
This feature is well established and works across many devices and browser versions. It has been available across browsers since 2021.
Safe to use without fallbacks.
57+
41+
12.1+
79+