Вариант 1:

#s4-ribbonrow{ display: none;}

Вариант 2 :

<style type="text/css">
    #s4-ribbonrow, .ms-cui-topBar2, .s4-notdlg, .s4-pr s4-ribbonrowhidetitle, .s4-notdlg noindex, #ms-cui-ribbonTopBars, #s4-titlerow, #s4-pr s4-notdlg s4-titlerowhidetitle, #s4-leftpanel-content {display:none !important;}
    .s4-ca{margin-left:0px !important; margin-right:0px !important;}
</style>