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When you are authoring a Card it is important to make sure that the styling associated with your Card cannot break out of the context of the card and affect the rest of the application. This is especially important when writing styles that would allow the card to open a "full screen" view. Traditionally when you are developing for the web and you are building applications that have the ability to got full-screen you would consider the viewport to be the same as the browser window's viewport, in Cardstack you cannot make this assumption. Depending on the circumstances, various parts of the Cardstack system will render your card in different ways, for example the Card Picker can render your card in a very small viewport intended to be used to chose the card during various types of searches.

To get around this limitation we can make use of the fixed-within-viewport component.


The fixed-within-viewport component can be used to position and size elements in either the actual browser viewport or a virtual viewport.

A typical example for an element that would usually be positioned and sized relative to the viewport is a mobile navigation:

mobile navigation

Here, the navigation sticks to the top of the viewport and remains there, even if the underlying document is scrolled. Likewise, when extended, it covers the complete viewport:

mobile navigation expanded

As we mentioned above, the viewport for a card is not necessarily always the actual browser viewport but might be something smaller than that. If the card containing the navigation is rendered inside a modal window above other content the, the navigation is to be positioned relative to that virtual viewport:

mobile navigation in virtual viewport

as well as sized relative to it when expanded:

mobile navigation expanded in virtual viewport


The fixed-within-viewport component is used to wrap the element that is supposed to be positioned and sized in relation to the viewport like this:

{{#fixed-within-viewport width="100vw" height="100vh"}}
  {{cardstack-content content=content.navigationCard format="embedded"}}

If no virtual viewport exists, positioning and sizing will be in relation to the browser viewport. If a virtual viewport exists that is marked with the data-virtual-viewport attribute, the fixed-within-component will position and size itself (and its contents) in relation to that element instead:

<div class="modal-window" data-virtual-viewport>
  {{#fixed-within-viewport width="100vw" height="100vh"}}
    {{cardstack-content content=content.navigationCard format="embedded"}}


The fixed-within-viewport component accepts a number of options to configure its position and size:

  • width: the width of the fixed element - the vw unit will be in relation to the virtual viewport if one exists
  • height: the height of the fixed element - the vh unit will be in relation to the virtual viewport if one exists
  • left: the offset from the left edge of the viewport - this will be in relation to the virtual viewport if one exists
  • top: the offset from the top edge of the viewport - this will be in relation to the virtual viewport if one exists
  • minWidth, maxWidth, minHeight, maxHeight: media queries that allow limiting the behavior of the fixed-within-viewport component to specific element sizes (e.g. to narrow viewports in the above mobile navigation examples); if the media query does not match, the fixed-within-viewport component simply renders a <div> with no attached styles or behavior