Z axis point of observation
perspective

Specify the distance from the user's point of observation to the Z axis when performing a transform.
Property values
Specify this property on the container
The distance from the z-plane to the observer's point of reference is specified using one of these units:
em | em | The font-size of the current font |
rem | relative em | The font-size of the <html> element |
in | inch | A size equal 96px |
px | pixels | A size equal to 1/96 inch |
pt | point | A size equal 1in/72 = 1.33px |
pc | pica | A size equal 1in/6 = 12pt = 16px |
cm | centimeter | A size equal to 96px/2.54 = 37.8px |
mm | millimeter | A size equal to 96px/25.4 = 3.8px |
Q | quarter millimeter | A size equal to 96px/1016 = 0.94px |
Smaller values put the observer closer to the object, shortening the vanishing point, giving it less of a 3D effect.
Larger values put the observer farther away from the object, lengthening the vanishing point, giving it more of a 3D effect.
Examples
perspective: 200px;