# PreAmp Mixer

PreAmp Mixer is VideoAmp's CSS framework.

## Structure

Mixer is broken into the following partial groups:

-   Helpers
-   Base
-   Components
-   Utilities

_Helpers_ includes helper styles such as colors, variables, mixins, functions, themes, typography and layout.

_Base_ contains styles for base HTML elements.

_Components_ contain styles for the PreAmp Core component library.

_Utilities_ includes utility styles for animations, Tailwind utilities, etc.

## Theming and Functional Classes

Mixer uses [Tailwind](https://tailwindcss.com/) to extend functional classes, making styling easy, clean and consistent. It also helps drive theming using CSS Custom Properties.

Themes are set up in the [themes](sass/mixer-helpers/_themes.scss) partial by modifying CSS custom property values scoped to a selector. For example `.va-dark` contains values for custom properties that override the values assigned to the `:root` level. Therefore, using the theme would require the addition of that theme's className added to the HTML element. A theme does not have to include overrides for all of the CSS custom property values, but any values not included will fall back to the defaults assigned to `:root`.

### CSS Custom Properties vs SASS Variables

The Tailwind framework requires the use of CSS Custom Properties to incorporate the property values in Javascript. One thing to note is that CSS Custom Properties are not interchangeable with SASS variables. Custom Properties are runtime variables, so when SASS is compiled, they have no value. That means that they cannot be used as values for SASS variables, functions or mixins.

### Functional Classes

Tailwind creates functional CSS classes that can be used for styling, however it is not recommended that they be used directly in HTML markup. Instead you can extend these classes in your SASS files:

```sass
.va-btn {
    @apply rounded py-2 px-4 font-normal text-va-button border-transparent border-2;
}
```

For more information on functional classes, visit the [Tailwind documentation](https://tailwindcss.com/docs/functions-and-directives/#apply)

## Helper Styles

### Color

The color palette and functionality are based on concepts from [react-md](https://react-md.mlaursen.com/customization/colors 'react-md').

Sass variables for each color are created from a function and can be used as `va-palette("COLOR", "HUE")`, or a specific example would be `va-palette("blue", "400")`.

There are also CSS Custom Properties available for each color. They can be used as `var(--va-blue-400)`.

A full list of the available colors can be found in the [colors](_colors.scss) partial.

### Typography

Typography styles can be applied with the following classes, the default sizes are listed for reference:

| className    | font-size                    |
| :----------- | :--------------------------- |
| `.u-title-1` | `font-size: 3.25rem` (52px)  |
| `.u-title-2` | `font-size: 2rem` (32px)     |
| `.u-title-3` | `font-size: 1.25rem` (20px)  |
| `.u-title-4` | `font-size: 1.125rem` (18px) |
| `.u-title-5` | `font-size: 1rem` (16px)     |
| `.u-body-1`  | `font-size: 0.875rem` (14px) |
| `.u-body-2`  | `font-size: 0.75rem` (12px)  |
| `.u-body-3`  | `font-size: 0.625rem` (10px) |
| `.u-body-4`  | `font-size: 0.5625rem` (9px) |

The default sizes of these helper classes can be changed using themes.

### Font-weight helper classes

| className        | font-weight        |
| ---------------- | ------------------ |
| `.u-font-thin`   | `font-weight: 200` |
| `.u-font-light`  | `font-weight: 300` |
| `.u-font-normal` | `font-weight: 400` |
| `.u-font-medium` | `font-weight: 500` |
| `.u-font-bold`   | `font-weight: 700` |

### Grid Layout

The Mixer grid layout is following and extending the Tailwind framework with some influence by Bootstrap's conventions. The grid is based on a 12 column grid using CSS Grid. The grid container must have the following classNames applied `va-grid` and either `va-columns-default` _or_ `va-columns-fluid`.

`va-columns-default` applies the 12 column grid that requires either 12 child elements, or fewer than 12 columns with the class `col-span-${n}` where the `${n}` are numbers that add up to 12.

`va-columns-fluid` allows you to have however many child elements you want and they will all equally fill the space.

#### Usage Example

A container div with the class `va-row` is required for the columns to work correctly. Only columns should be direct childeren of rows.

```tsx
<div className='va-grid va-columns-default'>
    <div className='col-span-12'>Full Width Column</div>
</div>
<div className='va-grid va-columns-default'>
    <div className='col-span-6'>50% Width Column</div>
    <div className='col-span-6'>50% Width Column</div>
</div>
<div className='va-grid va-columns-fluid'>
    <div>These columns</div>
    <div>Fill the space</div>
    <div>Evenly</div>
</div>
```

#### Gutters

By default the columns will have gutter spacing between them. The size of the gutter is configurable in the [`themes`](_themes.scss) partial (1.5rem or 24px by default). To remove the spacing, add the class `no-gutters` to the container element. For example:

```tsx
<div className="va-grid va-columns-default no-gutters">
    <div className="col-span-9">75% Width Column</div>
    <div className="col-span-3">25% Width Column</div>
</div>
```

### Responsive

Media queries follow the screen specifications set up in the Tailwind framework as `sm` `md` `lg` and `xl`. Including them as part of the class names will apply them based on minimum width, so they will apply to that breakpoint and all above it.

|              | `sm`            | `md`           | `lg`           | `xl`           |
| ------------ | --------------- | -------------- | -------------- | -------------- |
| Breakpoint   | 576px           | 768px          | 992px          | 1200px         |
| Class prefix | `.col-span-sm-` | `.col-span-md` | `.col-span-lg` | `.col-span-xl` |

For example, the following class additions:

```tsx
<div className="va-grid va-columns-default">
    <div className="col-span-sm-12 col-span-md-6 col-span-lg-3">
        Column Content
    </div>
</div>
```

Will adaptively render as the following:

| Browser Size                       | Column Width                    |
| ---------------------------------- | ------------------------------- |
| `sm` breakpoint to `md` breakpoint | 100% (applies `col-span-sm-12`) |
| `md` breakpoint to `lg` breakpoint | 50% (applies `col-span-md-6`)   |
| `lg` breakpoint and above          | 25% (applies `col-span-lg-3`)   |

### Utilities

Utility classes to assist in visual display and layout.

| className               | purpose                                                                 |
| ----------------------- | :---------------------------------------------------------------------- |
| `.va-sr-only`           | Only display content to screen readers                                  |
| `.va-sr-only-focusable` | Use with .va-sr-only to display screen reader content when it's focused |

Text inside the anchor will only be available to screenreaders and hidden from view.

```tsx
<a href="#">
    <span className="va-sr-only">Offscreen text</span>
</a>
```

Skip content link that is hidden from view but shown when it's focused.

```tsx
<a href="#main-content">
    <span className="va-sr-only va-sr-only-focusable">
        Skip to main content
    </span>
</a>
```

## Publishing

Publishes `dist/` to [https://www.npmjs.com/package/@preamp/mixer](https://www.npmjs.com/package/@preamp/mixer)

```
npm publish --access public
```

## Linking packages

For development in PreAmp, Mixer must be linked to the root directory in order for styles to be imported into documentation pages.

```bash
# Navigate to mixer and yarn link it

$ cd packages/mixer
$ yarn link

# Navigate back to root and link mixer

$ cd ../..
$ yarn link "@preamp/mixer"
```

For development in other applications, be sure to build the package of Mixer before linking.

```bash
# Navigate to mixer, build and create a link

$ cd packages/mixer
$ yarn build
$ yarn link
```