CSS Containment Generator - Optimize Rendering Performance

Contain Property

layout High Impact

Isolates the layout from the rest of the page. Nothing outside can affect its internal layout and vice versa.

paint High Impact

Contents won't be drawn outside its bounds. Browser can skip painting offscreen content.

size Medium Impact

Element can be sized without examining children. You must specify dimensions explicitly.

style Low Impact

CSS counters and quotes scoping. Prevents counter changes from leaking out.

content-visibility

Controls whether the browser renders element content. auto is great for long pages with offscreen content.

.container { /* Select containment options */ }

How CSS Containment Works

layout — Internal layout is independent; changes inside don't trigger reflow outside
paint — Creates a new stacking context; content clipped to padding box
size — Element sized without children; must set explicit width/height
style — Counters/quotes scoped to subtree; minimal perf gain alone

Container with containment applied

Child Element 1This element is inside the contained parent. Layout changes here won't affect siblings outside.

Child Element 2Paint containment clips this content to the container bounds.

Child Element 3With size containment, the parent ignores this element's size contribution.

Child Element 4Style containment scopes CSS counters within this subtree.

Layout Score

Paint Score

Overall

HIGH Add contain: layout paint to .card-list for 40% reflow reduction

MED Use content-visibility: auto on below-fold sections

MED Add contain: size to fixed-dimension containers

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