Many parts of default theme are selectable, while they shouldn't be.

[raqbit]

Simply holding your left mouse button on one place, and dragging across the page will select many elements of the login page. As far as I know the only thing that should be selectable is the input.

When selecting and grabbing the selection you can even move parts of the page.

Edit: This is happening with my install of Angergos GNOME, which at default has the default theme.

[FallingSnow]

This is a theme issue, so unless you are referring to one of the themes bundled with web-greeter, I suggest you contact the theme creator.

[raqbit]

This is an issue with the default theme shipping with Antergos using the GNOME desktop. (which is also the 'default' theme in this repo)