• CSS
  • Your first website: Styling the content
  • Challenge: Styling a biography page
  • Combinators
  • Sizing items in CSS
  • Styling tables
  • Challenge: A cool-looking box
  • Styling links
  • Introduction to CSS layout
  • CSS grid layout
  • CSS reference
  • Modules
    1. CSS basic user interface
    2. CSS cascading and inheritance
    3. CSS conditional rules
    4. CSS display
    5. CSS fonts
    6. CSS images
    7. CSS masking
    8. CSS namespaces
    9. CSS paged media
    10. CSS ruby layout
    11. CSS scroll-driven animations
    12. CSS shapes
    13. CSS text decoration
    14. CSS view transitions
    15. -moz-float-edge Non-standard Deprecated
    16. -moz-force-broken-image-icon Non-standard Deprecated
    17. -moz-image-region Non-standard
    18. -moz-orient Non-standard
    19. -moz-user-focus Non-standard Deprecated
    20. -moz-user-input Non-standard Deprecated
  • -webkit-*
    1. -webkit-border-before Non-standard
    2. -webkit-box-reflect Non-standard
    3. -webkit-mask-box-image Non-standard
    4. -webkit-mask-composite Non-standard
    5. -webkit-mask-position-x Non-standard
    6. -webkit-mask-position-y Non-standard
    7. -webkit-mask-repeat-x Non-standard
    8. -webkit-mask-repeat-y Non-standard
    9. -webkit-tap-highlight-color Non-standard
    10. -webkit-text-security Non-standard
    11. -webkit-touch-callout Non-standard
  • align-items
  • anchor-name Experimental
  • animation-*
    1. animation-direction
    2. animation-name
    3. animation-range Experimental
    4. animation-range-end Experimental
    5. animation-range-start Experimental
    6. animation-timeline Experimental
    7. backdrop-filter
    8. background-blend-mode
    9. background-origin
    10. background-repeat
    11. border-block
    12. border-block-end-style
    13. border-block-start-style
    14. border-bottom
    15. border-bottom-style
    16. border-end-end-radius
    17. border-image-repeat
    18. border-inline
    19. border-inline-end-style
    20. border-inline-start-style
    21. border-left
    22. border-radius
    23. border-right-width
    24. border-style
    25. border-top-right-radius
    26. bottom
    27. box-*
      1. box-align Non-standard Deprecated
      2. box-direction Non-standard Deprecated
      3. box-flex Non-standard Deprecated
      4. box-flex-group Non-standard Deprecated
      5. box-lines Non-standard Deprecated
      6. box-ordinal-group Non-standard Deprecated
      7. box-orient Non-standard Deprecated
      8. box-pack Non-standard Deprecated
      9. break-before
      10. clear
      11. clip-*
        1. clip Deprecated
        2. color-interpolation
        3. column-fill
        4. column-rule-style
        5. columns
        6. contain-*
          1. contain-intrinsic-inline-size
          2. container-name
          3. counter-increment
          4. cx
          5. display
          6. field-sizing Experimental
          7. fill-*
            1. filter
            2. flex-*
              1. flex-flow
              2. float
              3. font-family
              4. font-optical-sizing
              5. font-smooth Non-standard
              6. font-stretch Deprecated
              7. font-synthesis-position Experimental
              8. font-variant
              9. font-variant-emoji
              10. font-variation-settings
              11. grid
              12. grid-auto-rows
              13. grid-row
              14. grid-template-areas
              15. height
              16. image-orientation
              17. image-resolution Experimental
            3. inset-block
            4. inset-inline-end
            5. interpolate-size Experimental
            6. justify-self
          8. line-break
          9. line-height-step Experimental
        7. list-*
          1. list-style-type
        8. margin-*
          1. margin-block-start
          2. margin-inline-start
          3. margin-trim Experimental
        9. marker-*
          1. marker-start
        10. mask-*
          1. mask-border-outset
          2. mask-border-width
          3. mask-mode
          4. mask-size
          5. math-shift Experimental
          6. max-inline-size
          7. min-inline-size
          8. object-position
          9. offset-*
            1. offset-path
            2. order
            3. outline-offset
            4. overflow-anchor
            5. overflow-wrap
            6. overlay Experimental
            7. overscroll-*
              1. overscroll-behavior-x
              2. padding-block-end
              3. padding-inline-end
              4. padding-top
            8. page-*
              1. page-break-after Deprecated
              2. page-break-before Deprecated
              3. page-break-inside Deprecated
            9. place-content
            10. position
            11. position-anchor Experimental
            12. position-area Experimental
            13. position-try Experimental
            14. position-try-fallbacks Experimental
            15. position-try-order Experimental
            16. position-visibility Experimental
          10. resize
          11. ruby-align
          12. scale
          13. scroll-*
            1. scroll-margin-block-end
            2. scroll-margin-inline-end
            3. scroll-margin-top
            4. scroll-padding-block-start
            5. scroll-padding-inline-start
            6. scroll-snap-align
            7. scroll-timeline Experimental
            8. scroll-timeline-axis Experimental
            9. scroll-timeline-name Experimental
          14. scrollbar-*
            1. shape-image-threshold
            2. speak-as Experimental
            3. stroke-dasharray
            4. stroke-miterlimit
            5. table-layout
            6. text-*
              1. text-box
              2. text-decoration
              3. text-decoration-skip Experimental
              4. text-emphasis
              5. text-indent
              6. text-rendering
              7. text-size-adjust Experimental
              8. text-spacing-trim Experimental
              9. text-wrap
              10. timeline-scope Experimental
              11. transform-box
              12. transition-behavior
              13. transition-timing-function
            7. user-modify Non-standard Deprecated
            8. view-timeline Experimental
            9. view-timeline-axis Experimental
            10. view-timeline-inset Experimental
            11. view-timeline-name Experimental
            12. white-space-collapse
            13. word-break
            14. y
            15. Attribute selectors
            16. Universal selectors
          15. Combinators
            1. Column combinator Experimental
            2. Selector list
            3. :-moz-broken Non-standard Deprecated
            4. :-moz-drag-over Non-standard
            5. :-moz-first-node Experimental Non-standard
            6. :-moz-handler-blocked Non-standard
            7. :-moz-handler-crashed Non-standard
            8. :-moz-handler-disabled Non-standard
            9. :-moz-last-node Experimental Non-standard
            10. :-moz-loading Non-standard
            11. :-moz-locale-dir(ltr) Non-standard
            12. :-moz-locale-dir(rtl) Non-standard
            13. :-moz-only-whitespace Non-standard
            14. :-moz-submit-invalid Non-standard
            15. :-moz-suppressed Non-standard
            16. :-moz-user-disabled Non-standard
            17. :-moz-window-inactive Non-standard
          16. :blank Experimental
          17. :current Experimental
          18. :disabled
          19. :first-child
          20. :focus-within
        11. :has()
        12. :hover
        13. :is()
        14. :left
        15. :local-link Experimental
        16. :nth-child()
        17. :only-child
        18. :out-of-range
        19. :placeholder-shown
        20. :read-write
        21. :scope
        22. :target
        23. :target-within Experimental
        24. :visited
        25. ::-moz-color-swatch Non-standard
        26. ::-moz-focus-inner Experimental Non-standard
        27. ::-moz-list-bullet Experimental Non-standard
        28. ::-moz-list-number Experimental Non-standard
        29. ::-moz-meter-bar Non-standard
        30. ::-moz-progress-bar Experimental Non-standard
        31. ::-moz-range-progress Non-standard
        32. ::-moz-range-thumb Non-standard
        33. ::-moz-range-track Non-standard
      12. ::-webkit-*
        1. ::-webkit-inner-spin-button Non-standard
        2. ::-webkit-meter-bar Non-standard Deprecated
        3. ::-webkit-meter-even-less-good-value Non-standard
        4. ::-webkit-meter-inner-element Non-standard
        5. ::-webkit-meter-optimum-value Non-standard
        6. ::-webkit-meter-suboptimum-value Non-standard
        7. ::-webkit-progress-bar Non-standard
        8. ::-webkit-progress-inner-element Non-standard
        9. ::-webkit-progress-value Non-standard
        10. ::-webkit-scrollbar Non-standard
        11. ::-webkit-search-cancel-button Non-standard
        12. ::-webkit-search-results-button Non-standard
        13. ::-webkit-slider-runnable-track Non-standard
        14. ::-webkit-slider-thumb Non-standard
      13. ::cue
      14. ::first-line
      15. ::part()
      16. ::spelling-error
      17. ::view-transition-image-pair
      18. @color-profile
      19. @document Non-standard Deprecated
      20. @import
      21. @namespace
      22. @position-try Experimental
      23. @supports
      24. -moz-image-rect Non-standard Deprecated
      25. anchor-size() Experimental
      26. anchor() Experimental
      27. attr()
      28. calc-size() Experimental
      29. color-mix()
      30. cos()
      31. cubic-bezier()
      32. element() Experimental
      33. fit-content()
      34. hwb()
      35. inset()
      36. lch()
      37. log()
      38. min()
      39. oklch()
      40. palette-mix() Experimental
      41. scale3d()
      42. scroll() Experimental
      43. sin()
      44. steps()
      45. translateZ()
      46. view() Experimental
      47. <angle-percentage>
      48. <blend-mode>
      49. <color-interpolation-method>
      50. <custom-ident>
      51. <display-inside>
      52. <display-outside>
      53. <frequency-percentage>
      54. <hex-color>
      55. <image>
      56. <line-style>
      57. <overflow>
      58. <position-area> Experimental
      59. <resolution>
      60. <shape> Deprecated
      61. <time-percentage>
      62. Guides
      63. Animations
        1. Box alignment in block layout
        2. Introduction to the CSS basic box model
        3. Using relative colors
        4. Basic concepts of multi-column layout
        5. Handling content breaks in multi-column layout
      64. Conditional rules
        1. Using container size and style queries
      65. CSSOM view
        1. Introduction to formatting contexts
        2. Basic concepts of flexbox
        3. Controlling ratios of flex items along the main axis
        4. Variable fonts guide
      66. Grid
        1. Grid template areas
        2. Grids, logical values, and writing modes
        3. Masonry layout Experimental
      67. Images
        1. Basic concepts of logical properties and values
        2. Using CSS math functions
      68. Media queries
        1. Printing
      69. Nesting style rules
        1. Understanding z-index
      70. Scroll snap
        1. Basic shapes with shape-outside
        2. Using CSS transitions
      71. Center an element
      72. List group with badges
      73. Color picker tool
      74. Learn more
      75. See full compatibility
  • Experimental: This is an experimental technology
    Check the Browser compatibility table carefully before using this in production.

    The overlay <dialog> element) is actually rendered in the top layer. This property is only relevant within a list of transition-behavior.

    It is important to note that overlay can only be set by the browser — author styles cannot change the overlay value of any element. You can, however, add overlay to the list of transition properties set on an element. This causes its removal from the top layer to be deferred so it can be animated instead of disappearing immediately.

    Note: When transitioning overlay, you need to set discrete animations in that the visible (i.e. auto) state will always be shown for the full duration of the transition, regardless of whether it is the start or end state.

    Syntax

    css
    /* Keyword values */
    overlay: auto;
    overlay: none;
    
    /* Global values */
    display: inherit;
    display: initial;
    display: revert;
    display: revert-layer;
    display: unset;
    

    Values

    auto

    The element is rendered in the top layer if it is promoted to the top layer.

    none

    The element is not rendered in the top layer.

    Formal definition

    Animation typeDiscrete behavior except when animating to or from none is visible for the entire duration

    Formal syntax

    overlay = 
    none transitions from hidden to shown and back again.

    HTML

    The HTML contains a popovertarget attribute.

    html
    <button popovertarget="mypopover">Show the popover</button>
    <div popover="auto" id="mypopover">I'm a Popover! I should animate.</div>
    

    CSS

    The overlay property is only present in the list of transitioned properties. As overlay is a user-agent controlled property, it is not declared in the pre-transition or post-transition states.

    css
    html {
      font-family: Arial, Helvetica, sans-serif;
    }
    
    [popover]:popover-open {
      opacity: 1;
      transform: scaleX(1);
    }
    
    [popover] {
      font-size: 1.2rem;
      padding: 10px;
    
      /* Final state of the exit animation */
      opacity: 0;
      transform: scaleX(0);
    
      transition:
        opacity 0.7s,
        transform 0.7s,
        overlay 0.7s allow-discrete,
        display 0.7s allow-discrete;
      /* Equivalent to
      transition: all 0.7s allow-discrete; */
    }
    
    /* Needs to be included after the previous [popover]:popover-open
       rule to take effect, as the specificity is the same */
    @starting-style {
      [popover]:popover-open {
        opacity: 0;
        transform: scaleX(0);
      }
    }
    
    /* Transition for the popover's backdrop */
    
    [popover]::backdrop {
      background-color: rgb(0 0 0 / 0%);
      transition:
        display 0.7s allow-discrete,
        overlay 0.7s allow-discrete,
        background-color 0.7s;
      /* Equivalent to
      transition: all 0.7s allow-discrete; */
    }
    
    [popover]:popover-open::backdrop {
      background-color: rgb(0 0 0 / 25%);
    }
    
    /* Nesting selectors (&) cannot represent pseudo-elements, so this 
       starting-style rule cannot be nested. */
    
    @starting-style {
      [popover]:popover-open::backdrop {
        background-color: rgb(0 0 0 / 0%);
      }
    }
    

    The two properties we want to animate are transition property to animate between the two.

    Because the animated element is being promoted to the transition-behavior: allow-discrete value is also set in the shorthand to enable discrete transitions.

    The following steps are also required to get the animation working in both directions:

    • A starting state for the animation is set inside the @starting-style at-rule. This is needed to avoid unexpected behavior. By default transitions are not triggered on elements' first style updates, or when the display type changes from none to another type. @starting-style allows you to override that default in a specific controlled fashion. Without this, the entry animation would not occur and the popover would just appear.
    • display is also added to the list of transitioned elements so that the animated element is visible (set to display: block) throughout both the entry and exit animation. Without this, the exit animation would not be visible; in effect, the popover would just disappear. Again, transition-behavior: allow-discrete is required in this case for the animation to occur.

    You'll note that we've also included a transition on the ::backdrop that appears behind the popover when it opens, to provide a nice darkening animation. [popover]:popover-open::backdrop is needed to select the backdrop when the popover is open.

    Result

    The code renders as follows:

    Note: Because popovers change from display: none to display: block each time they are shown, the popover transitions from its @starting-style styles to its [popover]:popover-open styles every time the entry transition occurs. When the popover closes, it transitions from its [popover]:popover-open state to the default [popover] state.

    It is possible for the style transition on entry and exit to be different in such cases. See our Demonstration of when starting styles are used example for a proof of this.

    Specifications

    Specification
    CSS Positioned Layout Module Level 4
    # overlay

    Browser compatibility

    BCD tables only load in the browser

    See also