theme.park/docker-mods/jellyfin/root/etc/cont-init.d/98-themepark

#!/usr/bin/with-contenv bash

echo '-----------------------------'
echo '|  Jellyfin theme.park Mod  |'
echo '-----------------------------'

# Display variables for troubleshooting 
echo -e "Variables set:\\n\
'TP_DOMAIN'=${TP_DOMAIN}\\n\
'TP_COMMUNITY_THEME'=${TP_COMMUNITY_THEME}\\n\
'TP_THEME'=${TP_THEME}\\n"

# Set default
if [[ -z ${TP_DOMAIN} ]]; then
    echo 'No domain set, defaulting to theme-park.dev'
    TP_DOMAIN='theme-park.dev'
fi

THEME_TYPE='theme-options'
if [ "${TP_COMMUNITY_THEME}" = true ]; then
    THEME_TYPE='community-theme-options'
fi

case ${TP_DOMAIN} in
  *"github.io"*)
  echo "Switching to github.io URL style"
    TP_DOMAIN="${TP_DOMAIN}\/theme.park"
    ;;
esac

if [[ -z ${TP_THEME} ]]; then
    echo 'No theme set, defaulting to organizr'
    TP_THEME='organizr'
fi

# Adding stylesheets
if ! grep -q "${TP_DOMAIN}/css/base" /usr/share/jellyfin/web/index.html; then
    echo '---------------------------'
    echo '|  Adding the stylesheet  |'
    echo '---------------------------'
    sed -i "s/<\/body>/<link rel='stylesheet' href='https:\/\/${TP_DOMAIN}\/css\/base\/jellyfin\/jellyfin-base.css'><\/body> /g" /usr/share/jellyfin/web/index.html
    sed -i "s/<\/body>/<link rel='stylesheet' href='https:\/\/${TP_DOMAIN}\/css\/${THEME_TYPE}\/${TP_THEME}.css'><\/body> /g" /usr/share/jellyfin/web/index.html
    printf 'Stylesheet set to %s\n' "${TP_THEME}
    "
fi