JAVA

focus button

/* Focusing the button with a keyboard will show a dashed black line. */
button:focus-visible {
  outline: 4px dashed black;
}
  
/* Focusing the button with a mouse, touch, or stylus will show a subtle drop shadow. */
button:focus:not(:focus-visible) {
  outline: none;
  box-shadow: 1px 1px 5px rgba(1, 1, 0, .7);
}

focusbutton

frame.getRootPane().setDefaultButton(start);
start.requestFocus();