Broke my home assistant trying to get a background other then white

so i tried googling about changing the background color of the lovelace thing

well now its broken
i did what the instructions said
and in my configuration.yami

# Configure a default setup of Home Assistant (frontend, api, etc)
default_config:

# Text to speech
tts:
  - platform: google_translate

group: !include groups.yaml
automation: !include automations.yaml
#modem: !include modem.yaml
script: !include scripts.yaml
scene: !include scenes.yaml
#frontend: !include theme.yaml
#frontend:
  ... # your configuration.
#  themes: !include_dir_merge_named themes
  ... # your configuration.

  
  
homeassistant:
  customize: !include customize.yaml
  

my ui-lovelace-card.yaml file as i just trying things out

background: var(--background-image)
title: Home
resources:
  - url: /local/button-card.js
    type: module
    
  - type: 'custom:button-card'
    entity: switch.ac
    icon: mdi:air-conditioner
    color: rgb(28, 128, 199)

if i rem out the configuaration file the front end stuff i added and reboot doesnt help i get errors

error log

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2021-02-14 10:47:46 ERROR (SyncWorker_0) [homeassistant.util.yaml.loader] while parsing a block mapping
in "/config/configuration.yaml", line 2, column 1
expected <block end>, but found '<scalar>'
in "/config/configuration.yaml", line 15, column 3
2021-02-14 10:47:46 ERROR (MainThread) [homeassistant.bootstrap] Failed to parse configuration.yaml: while parsing a block mapping
in "/config/configuration.yaml", line 2, column 1
expected <block end>, but found '<scalar>'
in "/config/configuration.yaml", line 15, column 3. Activating safe mode

how do i fix it