 CSS transform

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.