What is "no-js" class?
<html class="no-js" lang="en" style="cursor: auto ! important;">
Is there another way (or better way) to identify the page is in the edit mode? I want to hide some elements in the edit mode using CSS.
In terms of concrete5, it's NOT a way to tell if the page is in edit mode.
There is a concrete5 function to test if you are in edit mode, and you can use that to add in an extra class. The following is an example of what you could do to your body tag in your template:
<?php $editmode = $c->isEditMode(); ?> <body class="<?php echo ($editmode ? 'editmode' : ''); ?>">
I often will make this a bit more useful, by putting in the page type handle in there as well: