Removed the border of code snippets.

assets/css/syntax.scss

@@ -12,12 +12,6 @@
 @import "_colors/dark-syntax";
 
 
-@mixin highlight-box-shadow($val) {
-  -moz-box-shadow: $val;
-  -webkit-box-shadow: $val;
-  box-shadow: $val;
-}
-
 html:not([mode]), html[mode=light] {
   @include light-syntax;
 }
@@ -56,12 +50,10 @@ html[mode=dark] {
 .highlight {
   @extend %code-snippet-radius;
   background: var(--highlight-bg-color);
-
   @at-root figure#{&} {
     background: var(--highlight-bg-color);
   }
   overflow: auto;
-  @include highlight-box-shadow(inset 0 0 2px #c2c6cc);
   .lineno {
     margin: .8rem 0rem;
     padding: 0 .5rem;
@@ -105,9 +97,8 @@ code {
   hyphens: none;
   &.highlighter-rouge {
     padding: 2px 4px;
-    margin: 0 .3rem;
+    margin: 0 .15rem;
     border-radius: 4px;
-    border: 1px solid var(--code-highlighter-rouge);
   }
   @at-root a>&.highlighter-rouge {
     padding-bottom: 0; // show link's underlinke