Custom css not working in child theme

Hello everybody,

I have an embarrassingly basic question. Searched the forum and online for ages but as I am an utter newbie at this still no joy.
I have the old v. 2.5.5 theme active and the simple custom.css plugin. I don’t expect to really need a child theme but everybody says I should make one for the latest Hueman. I am running old versions of WordPress and plugins need updating too. I daren’t try updating theme, WP and plugins that until I get the child theme working.

I pasted the custom.css code into the active Childify Me child style.css file, updated it, but it doesn’t work, the custom code effects for the sidebar disappeared.

Also do I then need to delete the Simple Custom.css plugin custom.css or can they both run without conflict? I tried keeping the the simple custom.css and the plugin. Will deleting the custom.css make it work?

This is what I pasted into the child theme.

.entry { color: black; }
.entry.excerpt { color: black; }

.entry .wp-caption { background: #ffffff; }
/* */ 
@media only screen and (min-width: 480px) and (max-width: 1200px) {
.s2-expand .s2 { background: #ffffff; }
}
@media only screen and (min-width: 480px) and (max-width: 960px) {
.s1-expand .s1 { background: #ffffff; }
}
@media only screen and (max-width: 479px) {
.sidebar { background: #ffffff; }
}

.sidebar-top p { float: left; color: #000000; font-size: 15px; font-weight: 600; text-transform: uppercase; line-height: 24px; padding: 3px 0; }

.s1 .sidebar-top, .s1 .sidebar-toggle { background-color: #fff!important; }

Any help getting this superb author’s site http://www.toniallenauthor.co.uk/ up to speed would be much appreciated.

Cheers!
Daniel