Darken bright elements in Alternative Dark theme (#3806)

- Table headers and box titles on the subscription management page use bright white backgrounds. This modifies these elements to use a dark background in order to be consistent with the rest of the theme.
- This also modifies tables to have dark borders.

p/themes/Alternative-Dark/adark.css

@@ -64,11 +64,11 @@ table {
 
 tr, th, td {
 	padding: 0.5em;
-	border: 1px solid #ddd;
+	border: 1px solid #333;
 }
 
 th {
-	background: #f6f6f6;
+	background: #262626;
 }
 
 form td,
@@ -454,7 +454,7 @@ a.btn {
 .box .box-title {
 	margin: 0;
 	padding: 5px 10px;
-	background: #f6f6f6;
+	background: #262626;
 	border: 1px solid #292929;
 	border-radius: 5px 5px 0 0;
 }

p/themes/Alternative-Dark/adark.rtl.css

@@ -64,11 +64,11 @@ table {
 
 tr, th, td {
 	padding: 0.5em;
-	border: 1px solid #ddd;
+	border: 1px solid #333;
 }
 
 th {
-	background: #f6f6f6;
+	background: #262626;
 }
 
 form td,
@@ -454,7 +454,7 @@ a.btn {
 .box .box-title {
 	margin: 0;
 	padding: 5px 10px;
-	background: #f6f6f6;
+	background: #262626;
 	border: 1px solid #292929;
 	border-radius: 5px 5px 0 0;
 }