Fix blacklists not working on /comments page.

This rule:

    .post-preview.blacklisted-active, #image-container.blacklisted-active, #c-comments .post.blacklisted-active {
      display: none;
    }

was being overridden by this rule:

    div#c-comments div#a-index div.post, div#c-comments div#a-show div.post {
      display: flex;
    }

app/javascript/src/styles/common/blacklists.scss

@@ -41,5 +41,5 @@
 }
 
 .post-preview.blacklisted-active, #image-container.blacklisted-active, #c-comments .post.blacklisted-active {
-  display: none;
+  display: none !important;
 }

test/system/blacklist_test.rb

@@ -0,0 +1,16 @@
+require "application_system_test_case"
+
+class BlacklistTest < ApplicationSystemTestCase
+  context "Blacklists" do
+    context "on the /comments page" do
+      should "hide the entire post" do
+        user = create(:user, created_at: 1.month.ago)
+        post = create(:post, tag_string: "spoilers")
+        comment = as(user) { create(:comment, post: post) }
+
+        visit comments_path
+        assert_selector ".post", visible: :hidden
+      end
+    end
+  end
+end