docs: update markdown code block

packages/vant-cli/site/common/style/highlight.less

@@ -71,7 +71,7 @@ pre {
 .hljs-selector-id,
 .hljs-selector-class,
 .hljs-strong {
-  color: #5299e0;
+  color: #4994df;
 }
 
 .hljs-emphasis {

packages/vant-cli/site/common/style/var.less

@@ -10,7 +10,7 @@
 @van-doc-dark-grey: #666;
 @van-doc-light-grey: #ccc;
 @van-doc-border-color: #f1f4f8;
-@van-doc-code-color: #455a64;
+@van-doc-code-color: #58727e;
 @van-doc-code-background-color: #f1f4f8;
 @van-doc-code-font-family: 'Source Code Pro', 'Monaco', 'Inconsolata', monospace;
 @van-doc-padding: 30px;

packages/vant-cli/site/desktop/components/Content.vue

@@ -189,6 +189,10 @@ export default {
     -webkit-font-smoothing: antialiased;
   }
 
+  p > code {
+    font-size: 14px;
+  }
+
   section {
     padding: 30px;
     overflow: hidden;