improved CM style

Signed-off-by: zhangtianli2006 <49156174+zhangtianli2006@users.noreply.github.com>

Author: ZTL-UwU

src/assets/code_mirror/tomorrow.css

@@ -72,6 +72,7 @@
 }
 
 .CodeMirror-linenumber {
+    color: #C0C4CC;
     font-size: 15px;
 }