style.css precedence (linky)

Embarrassed, but stuck on a simple issue…
I have a child theme ‘My_Mantra” and style.css in that folder, and the first two lines after the heading lines in my child style.css are:
@import url(“../mantra/style.css”);
#linky { z-index: -1; }

So why does my own style line above get over-ridden by the theme? Firebug shows
#linky { //site_url
display: block;
height: 120px;
position: absolute;
width: 1100px;
z-index: 1;
}
#linky { //style.css
z-index: -1; <–Firebug shows this with strikethru (over-ridden)
}