feat: add the ability to use system fonts

Author: aradzie

packages/keybr-themes/lib/fonts/index.less

@@ -118,6 +118,30 @@ html[data-font="ubuntu"] {
   --value-font-family: "Ubuntu Mono", monospace;
 }
 
+html[data-font="sans-serif"] {
+  --default-font-family: sans-serif;
+  --header-font-family: sans-serif;
+  --value-font-family: sans-serif;
+}
+
+html[data-font="serif"] {
+  --default-font-family: serif;
+  --header-font-family: serif;
+  --value-font-family: serif;
+}
+
+html[data-font="monospace"] {
+  --default-font-family: monospace;
+  --header-font-family: monospace;
+  --value-font-family: monospace;
+}
+
+html[data-font="cursive"] {
+  --default-font-family: cursive;
+  --header-font-family: cursive;
+  --value-font-family: cursive;
+}
+
 html {
   font-family: var(--default-font-family);
   font-size: 8px;

packages/keybr-themes/lib/themes/themes.ts

@@ -99,4 +99,20 @@ export const FONTS = new ThemeList([
     id: "cormorant",
     name: "Cormorant",
   },
+  {
+    id: "sans-serif",
+    name: "sans-serif (System)",
+  },
+  {
+    id: "serif",
+    name: "serif (System)",
+  },
+  {
+    id: "monospace",
+    name: "monospace (System)",
+  },
+  {
+    id: "cursive",
+    name: "cursive (System)",
+  },
 ]);