use a new has-text-default instead of has-text-black

bookwyrm/static/css/bookwyrm/utilities/_colors.scss

@@ -23,3 +23,8 @@
 .has-background-tertiary {
     background-color: $background-tertiary !important;
 }
+
+/* Workaround for dark theme as .has-text-black doesn't give desired effect. */
+.has-text-default {
+    color: $text !important;
+}

bookwyrm/static/css/themes/bookwyrm-dark.scss

@@ -53,6 +53,7 @@ $link-hover: $white-bis;
 $link-hover-border: #51595d;
 $link-focus: $white-bis;
 $link-active: $white-bis;
+$link-light: #0d1c26;
 
 /* bulma overrides */
 $background: $background-secondary;