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 Blue Theme that styles the AdapTable instance blue, with no border radius on the controls.
When the theme loads we leverage the VendorGridClassName property of Theme Predefined Config to tell AdapTable to load the AG Grid ag-theme-blue theme also.
Additionally, we also show a 'Custom Theme' which overrides even more CSS variables and changes layout around buttons in dialog footers and other details.