synchronized void install( Component c, int focusWidth ) {
			if( !(c instanceof JComponent) )
				return;

			this.focusWidth = focusWidth;

			JComponent jc = (JComponent) c;
			Border oldBorder = jc.getBorder();
			if( oldBorder == this )
				return; // already installed

			// component already has a padding border --> uninstall it
			// (may happen if single renderer instance is used in multiple comboboxes)
			if( oldBorder instanceof CellPaddingBorder )
				((CellPaddingBorder)oldBorder).uninstall();

			// this border can be installed only at one component
			// (may happen if a renderer returns varying components)
			uninstall();

			// remember component where this border was installed for uninstall
			rendererComponent = jc;

			// remember old border and replace it
			rendererBorder = jc.getBorder();
			jc.setBorder( this );
		}
Cell padding border used in popup list and for current value if not editable.
<p>
The insets are the union of the cell padding and the renderer border insets,
which vertically aligns text in popup list with text in combobox.
<p>
The renderer border is painted on the outer side of this border.
<p>
For button style "mac", also used to increase insets on left side for
"checked item" icon and to paint "checked item" icon for selected combobox item.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java