Fallback to monospace

Author: henrikekblad

src/assets/less/tree.less

@@ -1,7 +1,7 @@
 @content-padding: 1em; /* 树内容区域缩进2个英文字符, 此处1em为1个中文字符=2个英文字符 */
 
 .vjs__tree {
-  font-family: "Monaco", "Menlo", "Consolas", "Bitstream Vera Sans Mono";
+  font-family: "Monaco", "Menlo", "Consolas", "Bitstream Vera Sans Mono", monospace;
   font-size: 14px;
   .vjs__tree__content {
     padding-left: @content-padding;