Bug 1551696 - Fix a color for the deemphasized text of the field-label. r=MattN

Differential Revision: https://phabricator.services.mozilla.com/D31285

--HG--
extra : moz-landing-system : lando

browser/components/aboutlogins/content/components/login-item.css

@@ -40,7 +40,7 @@
 .field-label {
   display: block;
   font-size: smaller;
-  opacity: .7;
+  color: var(--in-content-deemphasized-text);
   margin-bottom: 5px;
 }