Improve layout of buttons for two factor auth

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

apps/twofactor_backupcodes/css/style.css

 .challenge {
 	margin-top: 0 !important;
 	margin-left: 0 !important;
+	box-sizing: border-box !important;
+	width: 100% !important;
 }
 
 .confirm-inline {
 	position: absolute;
-	right: 10px;
+	right: 0;
 	top: 0;
 	margin: 0 !important;
 	padding-right: 25px !important;

core/css/guest.css

 }
 .two-factor-link {
 	display: inline-block;
-	padding: 12px;
 	color: rgba(255, 255, 255, 0.75);
+	width: 100%;
+}
+.two-factor-link .button {
+	padding: 10px;
+	border-radius: 3px;
+	color: #555 !important;
+	display: inline-block;
+	margin: 5px 0;
+	text-align: center;
+	width: 100%;
+	box-sizing: border-box
 }
 
 /* Additional login options */
 	border-radius: 3px;
 	cursor: default;
 }
+.warning {
+	margin-top: 15px;
+}
 .warning.updateAnyways {
 	text-align: center;
 }