style: Update mackdown kbd style.

Author: jaywcjlove

src/styles/markdown.less

@@ -177,4 +177,18 @@
   .token.entity {
     cursor: help;
   }
+
+  kbd {
+    background-color: #fafbfc;
+    border-bottom-color: #d1d5da;
+    border: 1px solid #d1d5da;
+    border-radius: 3px;
+    box-shadow: inset 0 -1px 0 #d1d5da;
+    color: #24292e;
+    display: inline-block;
+    font-size: 11px;
+    line-height: 10px;
+    padding: 3px 5px;
+    vertical-align: middle;
+  }
 }