Box Model
The CSS box model explains an element’s size. Each box has content, padding, a border, and margin.
Another example
A 320px card no longer overflows after border-box includes its padding and border in that width.
Main parts
- 01Outer constraint
- 02Content and spacing model
- 03Computed size or reflow result
Use it when
Check the box model when the real size doesn't match the width or height you set.
Do not use it when
Never cover up a box-model mistake with numbers that have no clear reason.
Name used in code
box-sizing: border-box Before you ship
Check content order, shared design values, component consistency, contrast, zoom, and layout changes by screen size. Verify every theme, language, and state. If there is motion, offer an equal reduced-motion experience.
Outcome: Use or define Box Model to make the visual experience clear and easy to use. User context: A 320px card no longer overflows after border-box includes its padding and border in that width. Design concept to apply: Box Model. Why it fits: Check the box model when the real size doesn't match the width or height you set. Do not use it when: Never cover up a box-model mistake with numbers that have no clear reason. Design requirements: Set the content order, shared design values, and reusable components. Define how the layout changes by screen size and state. Keep useful design choices separate from decoration. Inclusion and resilience: Check contrast, zoom, languages, themes, and reduced motion when needed. Do not use color or effects as the only way to show meaning. Acceptance criteria: The design stays clear on phones and desktops, at zoom, in every theme, and in all supported languages. Interactive states stay clear and consistent. Evidence and limits (evidence boundary): A formal document may still be a draft, release candidate, or final version. Check its status and browser or platform support. Unknowns to confirm: Brand limits, amount of content, supported themes and languages, target devices, and design-system rules.
Check this request
Review the current use of Box Model. Definition: The CSS box model explains an element’s size. Each box has content, padding, a border, and margin. Release checks: Check content order, shared design values, component consistency, contrast, zoom, and layout changes by screen size. Verify every theme, language, and state. If there is motion, offer an equal reduced-motion experience. Before changing code, report the evidence you found, gaps, severity, and the smallest safe fix.