Tweak the highlight CSS to include more classes.

Specifically, 'kd' (declaration keyword) and 'cm' (multiline comment)

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

assets/scss/code.scss

@@ -77,7 +77,7 @@ pre code {
     }
 }
 
-.kr, .k {
+.kr, .kd, .k {
     font-weight: bold;
     @include var(color, code-keyword-color);
 }
@@ -87,6 +87,6 @@ pre code {
     @include var(color, code-type-color);
 }
 
-.c, .c1 {
+.c, .c1, .cm {
     color: $code-comment-color;
 }