Afterwars you need call the method in the init() function of the component. No reload the app and you will find the new button in the top right corner. Pressing will switch the theme to dark or back to light theme.
# install SQLite
npm i sqlite3 -D
# create db, save configuration in package.json, stores mock data into db
cds deploy --to sqlite:db/my-app.db
# test cds deploy command with --dry. Displays ever table and view it creates
cds deploy --to sqlite:db/my-app.db --dry
# get and overview of your tables with .tables
sqlite3 db/my-app.db .tables
# open and view newly created db
sqlite3 db/my-app.db -cmd .dump
# and select single field with
SELECT field FROM mytable WHERE mykeyfield= "00505601194D1EE9B7BFC518B85";
# update a field with
UPDATE mytable SET field = "test" WHERE mykeyfield= "00505601194D1EE9B7BFC518B85";