fix: added fallback font for $font-family-secondary

Author: Kirill Bolotsky

src/styles/variables.scss

@@ -1,6 +1,6 @@
 // Font families
 $font-family-primary: 'TT Norms Pro', sans-serif;
-$font-family-secondary: 'Roboto Mono', sans-serif;
+$font-family-secondary: 'Roboto Mono', Monaco, Consolas, mono;
 
 // Font sizes and line heights
 $font-size-base: 17px;