Note: This feature is available in Web Workers.
The z property of the CSSScale interface represents the z-component of the translating vector. A positive value moves the element towards the viewer, and a negative value farther away.
If this value is present, then the transform is a 3D transform and the is2D property will be set to false.
A CSSNumericValue. Can be set to a number, which is wrapped in a CSSUnitValue of unit: "number".
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