##<app-grid>
app-grid is a helper class useful for creating responsive, fluid grid layouts using custom properties.
Because custom properties can be defined inside a `@media` rule, you can customize the grid layout
for different breakpoints.
Example:
Within an element definition, import `app-grid-style.html`, then include the style sheet in the style
element inside the template.
```html
```
In this example, the grid will take 3 columns per row and only 1 column if the viewport width is
smaller than 640px.
### Expandible items
In many cases, it's useful to expand an item more than 1 column. To achieve this type of layout,
you can specify the number of columns the item should expand to by setting the custom property
`--app-grid-expandible-item`. To indicate which item should expand, apply the mixin
`--app-grid-expandible-item` to a rule with a selector to the item. For example:
```css
```
### Preserving the aspect ratio
When the size of a grid item should preserve the aspect ratio, you can add the `has-aspect-ratio`
attribute to the element with the class `.app-grid`. Now, every item element becomes a wrapper around
the item content. For example:
```css
```
### Styling
Custom property | Description | Default
----------------------------------------------|------------------------------------------------------------|------------------
`--app-grid-columns` | The number of columns per row. | 1
`--app-grid-gutter` | The space between two items. | 0px
`--app-grid-item-height` | The height of the items. | auto
`--app-grid-expandible-item-columns` | The number of columns an expandible item should expand to. | 1