Grid.js offers several built-in themes that allow you to quickly style tables without writing extensive CSS from scratch. These themes provide a polished, professional appearance and help your tables blend seamlessly into a variety of web project designs. The most common built-in themes include mermaid, default, and dark, each offering a distinct look and feel. Applying a theme is as simple as including the relevant Grid.js theme stylesheet in your HTML and referencing it when initializing your table.

You can further personalize your table by combining a built-in theme with your own custom CSS rules. This approach lets you preserve the structural styling and interactivity of the theme while adjusting specific visual elements—such as colors, fonts, or borders—to better match your project's branding or user interface guidelines. Custom CSS can target table headers, rows, or interactive controls, giving you fine-grained control over the table's appearance while still benefiting from the convenience of the built-in theme.