By default, each CSS property has its certain type of display in a page layout. For example, <div>, <h1> to <h6>, <p>, <form>, <header>, <footer>, and <section> by default behave like block-level elements. This means they block the entire width available, with a line break before and after the element. In other words, block-level elements don't welcome any "neighbors" in the same area with them. 

To set the block display for elements with other default values, you should use the display property with the block value.