feat: update style / exampleSite files and compatible with Hugo 0.58

assets/css/_core/_base.scss

@@ -73,9 +73,3 @@ a {
     }
   }
 }
-
-i.fas,
-i.far,
-i.fab {
-  padding: 0 .2rem;
-}

assets/css/_core/_normalize.scss

@@ -32,7 +32,9 @@ hr,
 h1,
 h2,
 h3,
-h4 {
+h4,
+h5,
+h6 {
   padding: 0;
   margin: 0;
 }

assets/css/_page/_post.scss

@@ -182,7 +182,10 @@
     }
   }
 
-  h3::before {
+  h3::before,
+  h4::before,
+  h5::before,
+  h6::before {
     content: "|";
     margin-right: .3125rem;
     color: $post-link-color;

assets/css/_partial/_post/_code.scss

@@ -108,7 +108,15 @@ p > code {
   }
 
   /* LineNumbersTable */  .lnt { color: $code-info-color; }
-  /* LineHighlight */  .hl { display: block; width: 100%; background-color: #ffffcc }
+  /* LineHighlight */  .hl {
+    display: block;
+    width: 100%;
+    background-color: darken($code-background-color, 5%);
+
+    .dark-theme & {
+      background-color: darken($code-background-color-dark, 5%);
+    }
+  }
   /* P */ .chroma .p { color: #A9A9B3 }
 
     /* Keyword */  .k { color: #859900 }