SharePoint 2013 Hide Left Hand Navigation Bar
Use below style to hide leftnav in SPO.
.ms-core-sideNavBox-removeLeftMargin
{
DISPLAY: none;
}
.ms-core-sideNavBox-removeLeftMargin
{
DISPLAY: none;
}
#contentBox
{
margin-left: 20px;
}
{
margin-left: 20px;
}