iOS Themes - Dark Mode and Light Mode from HACS


I am using iOS Themes - Dark Mode and Light Mode from HACS, but if I update Home Assistant, close my browser sessions (Firefox) it reverts back to the default theme. From what I read somewhere else this is saved within the browser. Can’t it be controlled somewhere else like an automation to set it? I have added the following to my configuration.yaml

themes: !include_dir_merge_named themes

The following is present in my lovelace-ui.yaml

background: var(–background-image)

background: var(--background-image)

Would prefer to keep the HA dashboard a little darker as I have light sensitivity to bright backgrounds.

Help appreciated