Fix contrast issue checkbox

- Fixed contrasting issue with tick check on custom fields, also fixed the ugly green tick coming up on the checklists in cards by utilisation of the !important tag to override it with the checkbox colour for custom fields also.

client/components/boards/boardColors.css

@@ -2544,8 +2544,8 @@ THEME - Exodark
   background: #1b1b1b;
 }
 .board-color-exodark .materialCheckBox.is-checked {
-  border-bottom: 2px solid #222;
-  border-right: 2px solid #222;
+  border-bottom: 2px solid #dbdbdb!important;/*Fix contrast of checkbox*/
+  border-right: 2px solid #dbdbdb!important;
 }
 .board-color-exodark .is-multiselection-active .multi-selection-checkbox.is-checked + .minicard {
   background: #e9e9e9;