By default, wordpress adds special admin bar in top of site. Maybe you want to remove it from all user’s accounts.
Use code
#wpadminbar { display:none;}html{margin-top:0 !important}
you can place this in theme options – general options – custom css
Sometimes, it will not help because some plugins can add additional bar. Usually, it’s Buddypress. So, disable it in Settings – Buddypress – Options – ToolBar