How to add square minimize and maximize buttons for Vaadin window

Flow
1

Hi Team,

I am using vaadin 8 and I would like to replace “+” button with square maximize button and “-” button to square minimize button for vaadin window. Can you guys help me out in getting those buttons for vaadin window.
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2

The style names of those buttons are “v-window-closebox” and “v-window-maximizebox”

You can try to style them like the follows to make them look more button like

.v-window-maximizebox {
   background: green;
   border-color: darkgreen;
   border-radius: 4px;
   border-style: groove;
   color: white;
   border: 2px;
}