Add item button

www/kanban/app-kanban.less

@@ -26,7 +26,7 @@
     @palette8: #E4CAFF;
 
     .kanban-board-header {
-        background-color: #AAA;
+        background-color: #c9c9c9;
     }
 
     .cp-kanban-palette-nocolor {
@@ -155,6 +155,8 @@
         }
 
         .kanban-board {
+            background-color: #eaeaea;
+            color: @cryptpad_text_col;
             header {
                 display: flex;
                 align-items: center;
@@ -174,6 +176,25 @@
                     cursor: move;
                 }
             }
+            footer {
+                padding: 10px;
+                span {
+                    .tools_unselectable();
+                    outline: none;
+                    width: 100%;
+                    border: 1px solid @cryptpad_text_col;
+                    border-radius: 0px;
+                    font-size: 40px;
+                    display: inline-flex;
+                    justify-content: center;
+                    align-items: center;
+                    line-height: 1;
+                    cursor: pointer;
+                    &:hover {
+                        background-color: rgba(0,0,0,0.1);
+                    }
+                }
+            }
         }
 
         #kanban-edit {