style: better top/bottom margin of horizontal line

Author: jeffreytse

_sass/yat/_layout.scss

@@ -479,14 +479,15 @@ html {
       margin: 60px 0 19px;
     }
 
-    p, hr {
+    p {
       margin-bottom: 24px;
     }
 
     hr {
       height: 1px;
       background-color: #ebebeb;
       border: none;
+      margin: 60px 0;
     }
   }