Simplify design, remove gradient and hover effect.
Horizontally centered enter button and logo.
Compact size when viewer width is less than
640 pixels or viewer height is less than
480 pixels.
Interactive (e.g. navigation, attribution) element have z-index 10.
Overlayed elements (slider, route bubble) have z-index 20.
Filling elements have z-index -1 to 9.
Cover have z-index 100.
Special elements (debug) have z-index 50.
Do not change z-index in server cssnano plugin (z-index are not
changed when built from npm script).
