The best thing you can do is to access the dev tools (often f12 in you keyboard) to view your container from your browser.
From there you can find out why your class isn't working.
There are multiple reasons why this isn't working like that your custom class isn't loaded (not imported in the main scss) or that other classes are overwriting your values.
Getting to know and work with dev tools is (almost) mandatory when you like to customize your styling