refactor: enhance the configurability of fonts (#986)

_sass/addon/commons.scss

@@ -34,7 +34,7 @@ body {
     env(safe-area-inset-bottom) env(safe-area-inset-left);
   color: var(--text-color);
   -webkit-font-smoothing: antialiased;
-  font-family: 'Source Sans Pro', 'Microsoft Yahei', sans-serif;
+  font-family: $font-family-base;
   line-height: 1.75;
 }
 

_sass/addon/module.scss

@@ -7,7 +7,7 @@
 %heading {
   color: var(--heading-color);
   font-weight: 400;
-  font-family: Lato, 'Microsoft Yahei', sans-serif;
+  font-family: $font-family-heading;
 }
 
 %section {

_sass/addon/variables.scss

@@ -28,3 +28,8 @@ $bottom-min-height: 35rem !default;
 /* syntax highlight */
 
 $code-font-size: 0.85rem !default;
+
+/* fonts */
+
+$font-family-base: 'Source Sans Pro', 'Microsoft Yahei', sans-serif;
+$font-family-heading: Lato, 'Microsoft Yahei', sans-serif;

_sass/jekyll-theme-chirpy.scss

@@ -10,9 +10,9 @@
   "colors/light-typography",
   "colors/dark-typography",
 
-  "addon/module",
   "addon/variables",
   "variables-hook",
+  "addon/module",
   "addon/syntax",
   "addon/commons",