In 'Settings/Users/Access management', enable the right:
'Manage CSS spreadsheet'

In 'Settings/General settings/CSS', you can enter CSS code that will replace the existing CSS code of your account.

More specifically, you can also provide CSS rules to the user in 'Settings/Users/Users' (field 'CSS').

Find below some examples of CSS code :

Goal	Code
Customize the design (ex: change left menu colors)	.nav-header { background: #000000; } body{ background-color: #000000; } nav #side-menu li.active { border-left: 4px solid #fff8c00; background: #808080; } .navbar-default .nav > li > form.input_nav:hover { background-color: #808080; } .btn-primary, .btn-info { background-color: #FFFFFF; border-color: #000000; color: #000000; }
Change size of product keys	.bt_express { width: 10%; }
Hide some data fields (ex: delete the Expiry date field when creating a customer in a sale)	#validite_client_modif_vente_tr {display: none; }
Set the ticket height on the sales interface	.vente_liste_produits { overflow-y: scroll; max-height: 20em; }
Rename button labels (ex : Next 1 in Starters)	#btn_ordo_2 span { display: none; } #btn_ordo_2:after { content: 'Entrées'; }