You can customize your dashboard in BoldBI using the provided variables to create a custom theme. Follow these steps:
Download the default light and dark files from the Github repository and extract them.
Copy all CSS files from the light folder inside the themes folder and paste them into a newly created folder. For example, create a new folder called darkviolet.

boldbi.application.definition.css and boldbi.core.definition.css files in an editor and customize the color code in the provided variables.

README.md on the Github repository to generate boldbi.theme.definition.min.css.
README.md file, you can find the theme files in the directory {src directory}/assets/theme/{theme directory name}/boldbi.theme.definition.min.css.