visibility Property

Notice that, in contrast to the display property, the object (an image in this case) still reserves its physical space when not visible.

sphere image

Mouseover this text to make the sphere disappear.

[to see the source code, right-click anywhere in the window]

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very very thanks to : MSDN Library - Web Development - HTML and CSS - Cascading Style Sheets (CSS) - CSS Referrence - Attributes - Positioning - visibilty