Fix CSS styling for buttons in customizeSlaveTrade

Fix styling for the controls on the customize slave trade screen.

The styling had lower priority than the global styling.

css/intro/customizeSlaveTrade.css

@@ -25,40 +25,42 @@
 }
 
 
-.plus-button {
+button.plus-button {
     background: rgba(0, 139, 0, 0.2);
     border-color: rgba(0, 139, 0, 0.3);
 }
 
-.minus-button {
+button.minus-button {
     background: rgba(184, 0, 0, 0.2);
     border-color: rgba(184, 0, 0, 0.3);
 }
 
-.zero-button {
+button.zero-button {
     background: rgba(0, 0, 255, 0.2);
     border-color: rgba(0, 0, 255, 0.3);
 }
-.set-button {
+
+button.set-button {
     background: rgba(255, 210, 0, 0.2);
     border-color: rgba(255, 210, 0, 0.3);
 }
 
-.plus-button:hover {
+button.plus-button:hover {
     background: rgba(0, 139, 0, 0.4);
     border-color: rgba(0, 139, 0, 0.3);
 }
 
-.minus-button:hover {
+button.minus-button:hover {
     background: rgba(184, 0, 0, 0.4);
     border-color: rgba(184, 0, 0, 0.3);
 }
 
-.zero-button:hover {
+button.zero-button:hover {
     background: rgba(0, 0, 255, 0.4);
     border-color: rgba(0, 0, 255, 0.3);
 }
-.set-button:hover {
+
+button.set-button:hover {
     background: rgba(255, 210, 0, 0.4);
     border-color: rgba(255, 210, 0, 0.3);
 }