How can I let a div fill 100% width if no other elements are beside it?

Question

I have simple markup like this (a tab menu):

Answer 1

Depending on what browsers you need to support, you may be able to use flexbox:

$('.tab').click(function() {
  $(this).css('display', 'none');
});

.container {
  display: flex;
}

.tab {
  border: 1px solid black;
  padding: 5px;
  flex: 1;
  margin: 5px;
}

Click a tab to remove it

   
Tab 1
   
Tab 2
   
Tab 3