Setting the option noClasses = false for [markup.highlight] in site/landing/config.toml requires a stylesheet to be available. This option is used in order to have two styles for light and dark mode of the documentation site. The stylesheet is stored in site/landing/assets/scss/_chroma.scss. Update the style if the Hugo version is changed:
Replace the content of [data-user-color-scheme='light'] with the output of hugo gen chromastyles --style=colorful, but keep the first line containing the setting of the background.
Replace the content of [data-user-color-scheme='dark'] with the output of hugo gen chromastyles --style=dracula, but keep the first line containing the setting of the background.