Left and right started as arbitrary concept based on where political parties sit in a parliament and they totally depend on the circumstances of the political system. In European history at the time democracies came into existence you could have separated idiological streams into e.g. republicans (as in people who aim for a republic) and monarchists. Also the more political parties with different topics there are the more difficult it gets to assign them to either left or right. As another commenter stated… dividing a political system into left and right helps to define a common „enemy“ which moves away the political discourse from other topics that matter.

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Does not answer your question but I just checked and you cannot customize the font in Mlem