overflow-y property was introduced in CSS3 for the purposes of setting the clipping behavior for the top and bottom edges of an element. It determines what to do when a box's contents are too big (vertically) to fit inside.
overflow-y property allows you to specify how the contents should be displayed in the event that it is too large for its outer container. In other words, the contents "overflow" on the "y" axis (i.e. the vertical axis). For example, you can specify that the outer container grows vertical scroll bars whenever the contents are too large to fit inside. Or you could specify that the contents should simply be hidden.
overflow-y property is used for the vertical axis (i.e. the top and bottom edges). To determine overflow behavior for the horizontal axis (i.e. the left and right edges), use the
overflow shorthand property to set the overflow behavior for both the horizontal and vertical axes at once.
|Try it yourself!||
|Applies to:||Non-replaced block-level elements and non-replaced 'inline-block' elements|
At the time of writing, CSS3 was still under development and browser support for many CSS3 properties was limited or non-existent. For maximum browser compatibility many web developers add browser-specific properties by using extensions such as
-webkit- for Safari and Google Chrome,
-ms- for Internet Explorer,
-moz- for Firefox,
-o- for Opera etc. As with any CSS property, if a browser doesn't support a proprietary extension, it will simply ignore it.
This practice is not recommended by the W3C, however in many cases, the only way you can test a property is to include the CSS extension that is compatible with your browser.
Be aware that if you choose to use the proprietary CSS extensions in a live environment, your code will not pass any W3C CSS validation, as the browser-specific properties are not valid W3C properties.
Many of the CSS3 examples on this website include these browser specific properties. If they weren't included, most of the examples wouldn't work for most users (at least, not until possibly years after the article was written).
The major browser manufacturers are working to support the W3C properties, and eventually, you will be able to omit these browser-specific properties.