how can i fix login screen? I don't delete any package.
Wow! That is a very good question. Lets take a look at your configuration files. If you run this command...
find /etc/lightdm/ -print -type f -exec cat '{}' \; -exec echo \;
it will output all of the files that are used to configure the behavior of your login screen. Here's the output of mine:
donn@donnslaptop ~> find /etc/lightdm/ -print -type f -exec cat '{}' \; -exec echo \;
/etc/lightdm/
/etc/lightdm/lightdm.conf.d
/etc/lightdm/users.conf
#
# User accounts configuration
#
# NOTE: If you have AccountsService installed on your system, then LightDM will
# use this instead and these settings will be ignored
#
# minimum-uid = Minimum UID required to be shown in greeter
# hidden-users = Users that are not shown to the user
# hidden-shells = Shells that indicate a user cannot login
#
[UserList]
minimum-uid=500
hidden-users=nobody nobody4 noaccess
hidden-shells=/bin/false /usr/sbin/nologin
/etc/lightdm/io.elementary.greeter.conf
[greeter]
#activate-numlock=true
#default-wallpaper=/usr/share/backgrounds/elementaryos-default
#high-contrast=false
#onscreen-keyboard=false
#screensaver-timeout=60
Perhaps some file got shuffled around and changed your theme.
lsb_release -a
. – Hasan♦ May 29 '19 at 9:10