Is there layout viewport in android chrome?

in my chrome 65.0.3325 on android 8.10,

I set css on a element:

position: fixed;
bottom: 0;

when I start input something in a input element, the keyboard popup, the element that positioned by fixed, will also "popup up", seem to position by visual viewport

as I remembered, the position:fixed, will position the element by the layout viewport;

why does it failure？