Add syntax highlighting, edit theme, and revise AdvMake documentation

assets/scss/common/_dark.scss

@@ -4,7 +4,7 @@
 
 $body-bg-dark: $gray-900;
 $body-overlay-dark: darken($body-bg-dark, 2.5%);
-$border-dark: darken($body-bg-dark, 2.5%);
+$border-dark: lighten($body-bg-dark, 8%);
 $body-color-dark: $gray-300;
 $dots-dark: darken($body-color-dark, 50%);
 
@@ -179,13 +179,17 @@ body.dark ::selection {
 }
 
 body.dark pre {
-  background: $body-overlay-dark;
-  color: $body-color-dark;
+  background: #282a36;
+  color: #f8f8f2;
 }
 
 body.dark code {
-  background: $body-overlay-dark;
-  color: $body-color-dark;
+  background: #282a36;
+  color: #f8f8f2;
+}
+
+body.dark hr {
+  border-top: 1px solid $border-dark;
 }
 
 body.dark blockquote {

assets/scss/components/_code.scss

@@ -8,8 +8,8 @@ samp {
 }
 
 pre {
-  background: $beige;
-  color: $black;
+  background: #282a36;
+  color: #f8f8f2;
   line-height: $line-height-lg;
   margin: 2rem 0;
   overflow: auto;
@@ -18,8 +18,8 @@ pre {
 }
 
 code {
-  background: $beige;
-  color: $black;
+  background: #282a36;
+  color: #f8f8f2;
   padding: 0.25rem 0.5rem;
 }
 

assets/scss/layouts/_sidebar.scss

@@ -85,6 +85,10 @@ a.docs-link {
   font-size: $font-size-base * 0.9375;
 }
 
+.page-links a code {
+  color: #dee2e6;
+}
+
 .docs-link:hover,
 .docs-link.active,
 .page-links a:hover {