font-face declarations must not use CSS variables for the src attribute

[petermuessig]

As reported by Hira Kshetry in the OpenUI5 Slack: https://openui5.slack.com/archives/C0A7MHSSJ/p1672783549112489, Icon Fonts don't work when using CSS variables.

I remember we discussed in the past, that the font-face declaration don't support variables in the src attribute. In this case, we might exclude the font-face declarations from the replacement with the CSS variables, when using less variables inside and furthermore manifest the concrete property value.

We should verify this part with the font-face and then adopt the plugin dependent on the result.

[i556484]

Related internal incident: 2270189546

[matz3]

Should be fixed via #257. Or is there something else not working?

[matz3]

Closing as it's already solved via #257