CSS Display The display property is the most important CSS property for controlling layout.
Block-level Elements <div> The display property specifies if/how an element is displayed.
<h1> - <h6> Every HTML element has a default display value depending on what type of element it is. The default display value for most elements is block or inline.
<p> A block-level element always starts on a new line and takes up the full width available (stretches out to the left and right as far as it can).
<form>
<header>
<footer>
<section>
Inline Elements <span> An inline element does not start on a new line and only takes up as much width as necessary.
<a> This is an inline <span> element inside a paragraph.
<img>
<video> Every element has a default display value. However, you can override this.
Changing an inline element to a block element, or vice versa, can be useful for making the page look a specific way, and still follow the web standards.
A common example is making inline <li> elements for horizontal menus:
<head>
<style>
li {
       display: inline;
}
display: inline; default Default value. Displays an element as an inline element (like <span>)    </style>
block; Displays an element as a block element (like <p>) </head>
none; The element will not be displayed at all (has no effect on layout) <body>
inline-block; Displays an element as an inline-level block container. <p>Display a list of links as a horizontal menu:</p>
The inside of this block is formatted as block-level box, and the element itself is formatted as an inline-level box <ul>
list-item; Let the element behave like a <li> element   <li><a href="/html/default.asp" target="_blank">HTML</a></li>
run-in; Displays an element as either block or inline, depending on context   <li><a href="/css/default.asp" target="_blank">CSS</a></li>
inline-flex; Displays an element as an inline-level flex container. New in CSS3   <li><a href="/js/default.asp" target="_blank">JavaScript</a></li>
table; Let the element behave like a <table> element </ul>
table-caption Let the element behave like a <caption> element </body>
table-caption Above code shows a horizontal menu.  If remove "display: inline;" or use "display: block;" then, it results a vertical menu.
table-column-group Note: Setting the display property of an element only changes how the element is displayed, NOT what kind of element it is. So, an inline element with display: block;is not allowed to have other block elements inside it.
table-header-group
… The following example displays <span> elements as block elements:
<head>
<style>
  span {
            display: block;
            border: 2px orange solid;
  }
</style>
<body>
<span> A display property with a value of "block" results in </span>
<span>a line break between the two elements.</span>
</body>
The "display: block;" makes <span>…</span> have the same effect as <p>…</p> and show two lines.Otherwise, only one line will be displayed. The added "border" makes this more clear.
Hiding an element can be done by setting the display property to none. The element will be hidden, and the page will be displayed as if the element is not there
<head>
<style>
   h2.hidden {
      display: none;
   }
</style>
<head>
<body>
<h1>This is a visible heading</h1>
<h2 class="hidden">This is a hidden heading</h2>
<p>Notice that the h2 element with display: none; does not take up any space.</p>
</body>
visibility:hidden; also hides an element.  However, the element will still take up the same space as before. The element will be hidden, but still affect the layout
h2.hidden {
    visibility: hidden;
}