overflow

This property is a shorthand for the following CSS properties:

• overflow-x
• overflow-y

/* Keyword values */
overflow: visible;
overflow: hidden;
overflow: clip;
overflow: scroll;
overflow: auto;
overflow: hidden visible;

/* Global values */
overflow: inherit;
overflow: initial;
overflow: revert;
overflow: revert-layer;
overflow: unset;

The overflow property is specified as one or two <overflow> keyword values. If only one keyword is specified, both overflow-x and overflow-y are set to the same value. If two keywords are specified, the first value applies to overflow-x in the horizontal direction and the second one applies to overflow-y in the vertical direction.

visible

Overflow content is not clipped and may be visible outside the element's padding box. The element box is not a scroll container. This is the default value of the overflow property.

hidden

Overflow content is clipped at the element's padding box. There are no scroll bars, and the clipped content is not visible (i.e., clipped content is hidden), but the content still exists. User agents do not add scroll bars and also do not allow users to view the content outside the clipped region by actions such as dragging on a touch screen or using the scroll wheel on a mouse. The content can be scrolled programmatically (for example, by linking to anchor text, by tabbing to a hidden yet focusable element, or by setting the value of the scrollLeft property or the scrollTo() method), in which case the element box is a scroll container.

clip

Overflow content is clipped at the element's overflow clip edge that is defined using the overflow-clip-margin property. As a result, content overflows the element's padding box by the <length> value of overflow-clip-margin or by 0px if not set. Overflow content outside the clipped region is not visible, user agents do not add a scroll bar, and programmatic scrolling is also not supported. No new formatting context is created. To establish a formatting context, use overflow: clip along with display: flow-root. The element box is not a scroll container.

scroll

Overflow content is clipped at the element's padding box, and overflow content can be scrolled into view using scroll bars. User agents display scroll bars whether or not any content is overflowing, so in the horizontal and vertical directions if the value applies to both directions. The use of this keyword, therefore, can prevent scroll bars from appearing and disappearing as content changes. Printers may still print overflow content. The element box is a scroll container.

auto

Overflow content is clipped at the element's padding box, and overflow content can be scrolled into view using scroll bars. Unlike scroll, user agents display scroll bars only if the content is overflowing. If content fits inside the element's padding box, it looks the same as with visible but still establishes a new formatting context. The element box is a scroll container.

Overflow options include hiding overflow content, enabling scroll bars to view overflow content or displaying the content flowing out of an element box into the surrounding area, and combinations there of.

The following nuances should be kept in mind while using the various keywords for overflow:

• Specifying a value other than visible (the default) or clip for overflow creates a new block formatting context. This is necessary for technical reasons; if a float intersects with a scrolling element, it would forcibly rewrap the content after each scroll step, leading to a slow scrolling experience.
• For an overflow setting to create the desired effect, the block-level element must have either a set height (height or max-height) if the overflow is in the vertical direction, a set width (width or max-width) if the overflow is in the horizontal direction, a set block-size ((block-size or max-block-size) if the overflow is in the block direction, or a a set inline-size ((inline-size or max-inline-size) or white-space set to nowrap if the overflow is in the inline direction.
• Setting overflow to visible in one direction (i.e. overflow-x or overflow-y) when it isn't set to visible or clip in the other direction results in the visible value behaving as auto.
• Setting overflow to clip in one direction when it isn't set to visible or clip in the other direction results in the clip value behaving as hidden.
• The JavaScript Element.scrollTop property may be used to scroll through content in a scroll container, except when overflow is set to clip.

overflow = 
  <'overflow-block'>{1,2}  

<overflow-block> = 
  visible  |
  hidden   |
  clip     |
  scroll   |
  auto     

HTML

<div>
  <code>visible</code>
  <p class="visible">
    Maya Angelou: "I've learned that people will forget what you said, people
    will forget what you did, but people will never forget how you made them
    feel."
  </p>
</div>

<div>
  <code>hidden</code>
  <p class="hidden">
    Maya Angelou: "I've learned that people will forget what you said, people
    will forget what you did, but people will never forget how you made them
    feel."
  </p>
</div>

<div>
  <code>clip</code>
  <p class="clip">
    Maya Angelou: "I've learned that people will forget what you said, people
    will forget what you did, but people will never forget how you made them
    feel."
  </p>
</div>

<div>
  <code>scroll</code>
  <p class="scroll">
    Maya Angelou: "I've learned that people will forget what you said, people
    will forget what you did, but people will never forget how you made them
    feel."
  </p>
</div>

<div>
  <code>auto</code>
  <p class="auto">
    Maya Angelou: "I've learned that people will forget what you said, people
    will forget what you did, but people will never forget how you made them
    feel."
  </p>
</div>

<div>
  <code>overlay</code>
  <p class="overlay">
    Maya Angelou: "I've learned that people will forget what you said, people
    will forget what you did, but people will never forget how you made them
    feel."
  </p>
</div>

CSS

body {
  display: flex;
  flex-wrap: wrap;
  justify-content: start;
}

div {
  margin: 2em;
  font-size: 1.2em;
}

p {
  width: 5em;
  height: 5em;
  border: dotted;
  margin-top: 0.5em;
}

div:nth-of-type(5),
div:nth-of-type(6) {
  margin-top: 200px;
}

p.visible {
  overflow: visible;
}

p.hidden {
  overflow: hidden;
}

p.clip {
  overflow: clip;
  overflow-clip-margin: 1em;
}

p.scroll {
  overflow: scroll;
}

p.auto {
  overflow: auto;
}

p.overlay {
  overflow: overlay;
}

Result

A scrolling content area cannot be scrolled by a keyboard-only user, with the exception of users on Firefox (which makes the container keyboard focusable by default).

As a developer, to allow non-Firefox keyboard-only users to scroll the container, you will need to give it a tabindex using tabindex="0". Unfortunately, when a screen reader encounters this tab-stop, they will have no context for what it is and their screen reader will likely announce the entirety of its contents. Giving it an appropriate WAI-ARIA role (role="region", for example) and an accessible name (via aria-label or aria-labelledby) can mitigate this.

• overflow-x, overflow-y
• overflow-block, overflow-clip-margin, overflow-inline
• clip, display, text-overflow, white-space
• CSS overflow
• Keyboard-only scrolling areas on adrianroselli.com (2022)