AdapTable ships with 2 themes - Dark or Light. But you can create your own theme yourself through the use of CSS variables. 
We provide many properties for you to set when creating your theme; most are colour based, but you have control also over button shapes and sizes for example.
In this example we have created a 'Wimbledon Theme' that styles the AdapTable instance purple and green, with slightly rounded borders. Note that we use Row Styles to similarly colour the grid).
We have also created a 'Blue Theme'. When this loads we leverage the VendorGridClassName of Theme Predefined Config to tell AdapTable to load the ag-Grid ag-theme-blue theme also.