You can find out what design theme is currently active in your store via the Themes page of your store's Admin area (Store Design > Themes).
Your store's current theme is shown at the top of the page.
If you see an 'Edit custom options' link next to the name of your store's current theme, it means that the theme has some custom options that you can adjust. The link will get you to the settings page for the current theme where you will be able to specify your preferences. If you choose to readjust any settings on that page, be sure to save your changes.
Below the information about your store's current theme, a button titled Customize storefront is provided; you can use this button to access the Storefront Builder - a comprehensive tool that you can use to adjust and customize this theme and the design of your store in general.