box-sizing
Layout
Decides whether width includes padding and border; border-box is the easier one to reason about.
| How to write it | box-sizing: content-box; |
|---|---|
| Common values | content-box, border-box |
| Inherited | No — it stops at this element |
| Category | Layout |
How to read this
- An inherited property only needs writing once on the parent — every child picks it up. Most text properties work this way.
- A shorthand resets whatever you leave out. Writing background: red alone also wipes a background image you set earlier.
- When rules collide, the more specific selector wins; only when specificity ties does source order decide.
- Animate transform and opacity for smoothness. Changing width or top forces the layout to be recalculated.
Frequently asked questions
Q. What is the CSS box-sizing property?
Decides whether width includes padding and border; border-box is the easier one to reason about.
Q. How do you write box-sizing?
As box-sizing: content-box; Common values include content-box, border-box.
Q. Is box-sizing inherited?
No. It applies only where you write it, so each element needs its own declaration.
Q. What group does box-sizing belong to?
The layout group.