I pasted some css into a usenet post and sent it; Usenapp ate everything except the terminal }
Message-ID: m2upqkFdjc7U1@mid.individual.net

Then I pasted it again and this time selected it, chose Quote Level, Increase. Usenapp scattered it with html
Message-ID: m2uq4gFdkshU1@mid.individual.net

The text in question was just this. It looked fine in the editor:
/* Hide the top tab bar */
#main-window[tabsintitlebar="true"]:not([extradragspace="true"]) #TabsToolbar {
opacity: 0;
pointer-events: none;
}
#main-window:not([tabsintitlebar="true"]) #TabsToolbar {
visibility: collapse !important;
}
/* Hide the sidebar top label */
#sidebar-header {
display: none;
}