All I did was installed bulma
yarn add bulma
Then imported bulma css
import "bulma/css/bulma.css"
And this is the error I get

does bulma rely on css properties?
@jquense Yes, they do use custom css properties. Is that a problem ?
No, just trying to understand the issue a bit. I think the problem is here that the default css setup adds a bunch of cssNext setup along with it, which isn't a great default..
I just ran into the same issue. I created a local copy of the gatsby postcss sass plugin and ripped out the postcss (since I don't need it).
@mbfisher had to add one more step to get that to work:
"gatsby-plugin-sass" to plugins: in gatsby-config.jsDue to the high volume of issues, we're closing out older ones without recent activity. Please open a new issue if you need help!
Most helpful comment
Posting my solution to this for others:
gatsby-plugin-sass(see here)layouts/index.scss(see here)index.scssinlayouts/index.js