Stop avatar text bleeding through in groups. Fixes #146.

Author: knadh

src/css/avatar.css

@@ -31,6 +31,7 @@
         margin: 0;
 
         & figure[data-variant="avatar"] {
+            isolation: isolate;
             margin-inline-end: calc(var(--space-5) * -1);
             border: 2px solid var(--background);