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The CSS border box is the rectangle bounded by the outer border edges in the CSS box model. It includes the content area, padding and borders, while excluding margins.^[ref]

For a simple unfragmented box, let the CSS content box be $120$ by $40$ CSS pixels, padding be $8$ pixels on every side, and borders be $2$ pixels on every side. The border dimensions areAdding six-pixel left and right margins would give a CSS margin box width of $152$, without changing the $140$-pixel CSS border box width.

The sizing edge matters when reversing this calculation. With box-sizing: border-box; width: 140px and the same padding and borders, the content width is $120$ pixels. With content-box sizing, a declaration width: 140px would instead produce a $160$-pixel CSS border box width, assuming no other constraint.

A CSS border box is a layout region, not a claim that every point inside it is opaque or that nothing paints outside it. Border style and color affect appearance, and CSS overflow concerns content extending beyond a box. Distinguishing geometry from painting avoids treating a screenshot's visible ink as a complete measurement of layout size.

The CSS box model describes the content, padding, border and margin regions used to lay out generated boxes. These define a CSS content box, CSS padding box, CSS border box and CSS margin box respectively. A box's declared width must be interpreted together with the applicable sizing rules.^[ref]

For a simple horizontal box with content width $w$, left/right padding $p_l,p_r$, border widths $b_l,b_r$ and margins $m_l,m_r$, the total margin-box width isWith $w=100$, padding ten on each side, borders two on each side and margins ten on each side, the total is 144 CSS pixels. Its border box is 124 pixels wide.

CSS box-sizing changes which area a width declaration sizes. With the same padding and borders but box-sizing: border-box; width: 100px, the border box is 100 pixels and the content width is 76 pixels in this example. Margins are still outside that declared border-box size.^[ref]

The example assumes ordinary nonnegative fixed horizontal values. Vertical margins can participate in CSS margin collapsing, and an inline element split across lines can generate several fragments. The box model supplies the regions; the formatting context determines how particular boxes are generated and positioned.

A CSS transform changes the coordinate mapping used to render a transformable element. Translation, scaling and rotation are examples of CSS transform functions. Their composition maps local points into the parent coordinate system; the CSS transform origin specifies the point around which the transformation is constructed.^[ref]

For an own two-dimensional example, use an ordinary CSS box with transform-box: border-box; transform-origin: 0 0;, no ancestor transforms, and local coordinates relative to that top-left origin. This fixes the CSS transform reference box and origin explicitly. Ignore the box's placement offset to isolate the transform itself.

Using homogeneous column vectors, letThe list transform: translate(10px, 0) scale(2); gives the product $TS$. Applied to point $(3,4,1{)}^{\mathsf{T}}$, the scale acts first:Reversing the list to scale(2) translate(10px, 0) gives $ST$ and the result $(26,8,1{)}^{\mathsf{T}}$. The translation is scaled in the reversed composition. Matrix multiplication explains the order dependence.^[ref]

The zero origin is part of the example, not an irrelevant decoration. A different origin adds translations around the listed operations and can change the mapped point. The simple matrix computation also fixes its column-vector convention instead of relying on an ambiguous phrase such as applying functions in order.

For boxes governed by the CSS box model, a transform changes rendering without rearranging the surrounding normal-flow content. It can nevertheless extend CSS overflow, and transformed geometry affects client rectangles. The absence of normal-flow re-layout is therefore not a claim that every geometrical or scrolling quantity stays fixed.^[ref]

The same transformed bounds matter when constructing a CSS scroll snap area. A rendered border can be rotated while its axis-aligned bounding box is used for alignment geometry. Separating layout boxes, coordinate mappings and derived bounds makes these effects easier to calculate.

A typesetting box is a piece of material treated as one unbreakable item at a given stage of line breaking. The simple paragraph model assigns it a width. A word already assembled from glyphs, or a small diagram placed within text, can be represented by such an item.^[ref]

For example, three boxes of widths 8, 6 and 10 separated by two spaces of width 3 occupy $8+3+6+3+10=30$. Keeping the boxes fixed while changing only the spaces is the model used by typesetting glue. If hyphenation makes an internal split available, the word must instead be represented with that discretionary break; a single indivisible box would hide the choice.

A box's width describes layout advance, which need not equal the exact ink extent of its glyphs. A more complete TeX box also has height and depth relative to a text baseline. These measurements allow boxes to be combined while maintaining baseline geometry.^[ref] The CSS box model uses its own rules for content, padding, borders and margins; interpreting every CSS box as an indivisible paragraph item would lose those distinctions.