Meta Post - Common CSS Hacks

[gafsiqueira]

@lizardmenfromspace

.cm-hmd-list-indent .cm-tab, ul ul { position: relative; }
.cm-hmd-list-indent .cm-tab::before, ul ul::before {
 content:'';
 border-left: 1px solid rgba(0, 122, 255, 0.25);
 position: absolute;
}
.cm-hmd-list-indent .cm-tab::before { left: 0; top: -5px; bottom: -4px; 
}
ul ul::before { left: -11px; top: 0; bottom: 0; 
} 

Sorry, I’m new to this CSS thing. Where exactly should I paste this code?
Thanks in advance.