Based on your screenshots, the font style is set by an external screen.min.css file.
In general, the report is processed and rendered in HTML on the server. The HTML is delivered at the client and then it is loaded in the viewer. The report's HTML goes along with default CSS rules. If there are external stylesheets overriding the default styles, please consider excluding the external CSS or changing the selectors to avoid affecting the report's HTML.
Other approach will be to export the report in PDF and to load it in browser e.g. this example
I hope this information is helpful.
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