I looked further, and you are right, it’s not the CSS.
After I have activated your plugin, when I view the Admin->Posts, I get the following error which happens after the title of the very first post is shown.
Uncaught TypeError: $(…).datepicker is not a function
at HTMLDocument.<anonymous> (applyonline-admin.js?ver=1.9.8:33)
at i (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,moxiejs,plupload&ver=4.9.5:2)
at Object.fireWith [as resolveWith] (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,moxiejs,plupload&ver=4.9.5:2)
at Function.ready (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,moxiejs,plupload&ver=4.9.5:2)
at HTMLDocument.K (load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable,moxiejs,plupload&ver=4.9.5:2)
edit.php:1 Failed to load resource: the server responded with a status of 500 ()