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

You can use display:table and display:table-cell see below code

HTML:

   
Tab 1
   
Tab 2
   
Tab 3

CSS:

.container {
  display: table;
  width:100%;
}

.tab {
  border: 1px solid black;
  padding: 5px;
  display: table-cell;
  margin: 5px;
}