Full page post template for Oxygen

Hi, I use the online editing interface. I would like my post pages to be full width with no sidebars, is this possible, and if so, how would I do it using the online editor. I tried to put the lines in the CSS edit box (to remove secondary) by just adding this:

.singular-post #sidebar-secondary {
display: none;
}

.singular-post #content {
width: 100%;
}
but it did not work…P.S. the “none,” is in red.