small dark-mode fixes

build/scss/_cards.scss

@@ -483,8 +483,12 @@ html.maximized-card {
 
   .card {
     background-color: $dark;
-    color: color-yiq($dark);
+    color: $white;
 
+    .card {
+      background-color: lighten($dark, 5%);
+      color: $white;
+    }
     .nav.flex-column > li {
       border-bottom-color: $gray-600;
     }

build/scss/_colors.scss

@@ -95,7 +95,10 @@ a.text-muted:hover {
     background-color: lighten($dark, 7.5%) !important;
     color: $white !important;
   }
-  .link-black {
+  .text-black,
+  .text-dark,
+  .link-black,
+  .link-dark {
     color: $gray-400;
   }
 }