feat(first-screen): add background_img_dark configuration item

_config.yml

@@ -46,9 +46,12 @@ style:
 first_screen:
   enable: false  # Option values: true | false
 
-  # First screen background image (You can use local image or image external link)
+  # First screen background image (You can use local image path or image link)
   background_img: /images/bg.svg
 
+  # First screen background image in dark mode (You can use local image path or image link)
+  background_img_dark: /images/bg.svg
+
   # First screen description
   # You can use the "||" to begin a newline, maximum is two lines.
   description: Keep writing and Keep loving.

source/css/layout/_partial/first-screen.styl

@@ -1,17 +1,24 @@
 if (hexo-config('first_screen')) {
-  $temp-img = hexo-config('first_screen.background_img')
+  $temp-fs-bg-img-light = hexo-config('first_screen.background_img')
+  $temp-fs-bg-img-dark = hexo-config('first_screen.background_img_dark')
 }
 else {
-  $temp-img = ''
+  $temp-fs-bg-img-light = ''
+  $temp-fs-bg-img-dark = ''
 }
 
-$first-screen-img = $temp-img ? $temp-img : '/images/bg.svg'
+$fs-bg-img-light = $temp-fs-bg-img-light ? $temp-fs-bg-img-light : '/images/bg.svg'
+$fs-bg-img-dark = $temp-fs-bg-img-dark ? $temp-fs-bg-img-dark : $fs-bg-img-light
 
 .first-screen-container {
   width 100%
   height 100vh
   overflow hidden
-  background url($first-screen-img) center center / cover no-repeat
+  background url($fs-bg-img-light) center center / cover no-repeat
+
+  .dark-mode & {
+    background url($fs-bg-img-dark) center center / cover no-repeat
+  }
 
   .first-screen-content {
     display flex