Bulma is readily customizable via Sass variables. Any of the variables used by Bulma can be changed by modifying the assets/styles/site-bulma.scss file.

Try adding the following lines to the top of your file to see how it changes things:

$primary: #2e7636;  // change primary color to green
$body-color: #00008B;  // change main text to blue

You’ll have to run npm run dev to see the changes take. For more details on building the CSS files, see the front end documentation.