allow overriding theme fonts

src/routes/api/fonts.js

@@ -0,0 +1,33 @@
+const optionService = require('../../services/options');
+
+function getFontCss(req, res) {
+    res.setHeader('Content-Type', 'text/css');
+
+    if (!optionService.getOptionBool('overrideThemeFonts')) {
+        res.send('');
+
+        return;
+    }
+
+    const optionsMap = optionService.getOptionsMap();
+
+    // using body to be more specific than themes' :root
+    res.send(`
+body {
+    --main-font-family: ${optionsMap.mainFontFamily};
+    --main-font-size: ${optionsMap.mainFontSize}%;
+     
+    --tree-font-family: ${optionsMap.treeFontFamily};
+    --tree-font-size: ${optionsMap.treeFontSize}%; 
+    
+    --detail-font-family: ${optionsMap.detailFontFamily};
+    --detail-font-size: ${optionsMap.detailFontSize}%;
+    
+    --monospace-font-family: ${optionsMap.monospaceFontFamily};
+    --monospace-font-size: ${optionsMap.monospaceFontSize};
+}`);
+}
+
+module.exports = {
+    getFontCss
+};