overflow

Generally, the content of a block box is confined to the content edges of the box. In certain cases, a box may overflow, meaning its content lies partly or entirely outside of the box, e.g.:

Whenever overflow occurs, the 'overflow' property specifies whether a box is clipped to its padding edge, and if so, whether a scrolling mechanism is provided to access any clipped out content.

The positioning block is the viewport, a block which is an ancestor of the aqua box, so overflow:hidden does not clip the pink box which is a absolutely positioned element nested in the aqua box. You should find the pink box just below the fold.

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The three boxes are nested inside each other.

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aqua
yellow
pink

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<div id="aqua">aqua     <div id="yellow">yellow         <div id="pink">pink</div>     </div> </div>

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Use shift + enter to create new lines (even in Safari and Chrome).