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Update styling docs (#1339)

Building on https://github.com/lensapp/lens/pull/1267 and iterating on the docs,
re-organizing them into Layout and Theme sections.

Also adding sample code on how to detect theme changes in JavaScript.

Signed-off-by: Stefan Cameron <stefancameron@SC-MBPt13-2018.austin.rr.com>
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@ -127,4 +127,4 @@ You can use CSS variables generated from theme `.json` files to style an extensi
- `radioActiveBackground`: background color for active radio buttons.
- `menuActiveBackground`: background color for active menu items.
In most cases you would only need base, text and some of the layout colors.
In most cases you would only need base, text and some of the layout colors.

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@ -1,15 +1,18 @@
# Styling an extension
Lens provides a set of global styles and UI components that can be used by any extension to preserve look and feel of the application.
## Styling approach
Lens heavily uses SCSS preprocessor with a set of predefined variables and mixins.
Lens provides a set of global styles and UI components that can be used by any extension to preserve the look and feel of the application.
## Layout
For layout tasks Lens is using [flex.box](https://www.npmjs.com/package/flex.box) library which provides helpful class names to specify some of the [flexbox](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Flexible_Box_Layout/Basic_Concepts_of_Flexbox) properties. For example, `div` with class names:
```
```html
<div className="flex column align-center"></div>
```
at the end will have following css properties:
```
```css
div {
display: flex;
flex-direction: column;
@ -19,81 +22,131 @@ div {
However, feel free to use any styling technique or framework like [Emotion](https://github.com/emotion-js/emotion) or just plain CSS if you prefer.
## Themes
Lens using 2 built-in themes located in `src/renderer/themes` folder each for light and dark color schemes. Active theme can be changed in the `Preferences` page.
![Color Theme](images/theme-selector.png)
### Layout Variables
When Lens gets loaded it transforms selected theme `json` file into list of [CSS Custom Properties (CSS Variables)](https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties) which then gets injected into `:root` element so any of the down-level components can use them.
![CSS vars listed in devtools](images/css-vars-in-devtools.png)
There is a set of CSS Variables available for extensions to use for basic layout needs. They are located inside `:root` and are defined in [app.scss](https://github.com/lensapp/lens/blob/master/src/renderer/components/app.scss):
When user changes a theme, the process is repeated, new css variables appear instead of previous ones.
If you want to follow a selected theme to keep the 'native' Lens look and feel, respecting the light/dark appearance of your extension, you can use provided variables and build-in lens components such as buttons, dropdowns, checkboxes etc.
## Injected styles
Every extention is affected by list of default global styles defined in `src/renderer/components/app.scss`. These are basic browser resets like setting `box-sizing` property for every element, default text and background colors, default font size, basic headings visualisation etc.
Extension may overwrite them if needed.
## Variables to use
### Basic styling
There is a list of CSS Variables available for extension to use. Basic variables located inside `:root` selected in `src/renderer/components/app.scss`:
```
--unit: 8px;
--padding: var(--unit);
--margin: var(--unit);
--border-radius: 3px;
--font-main: 'Roboto', 'Helvetica', 'Arial', sans-serif;
--font-monospace: Lucida Console, Monaco, Consolas, monospace;
--font-size-small: calc(1.5 * var(--unit));
--font-size: calc(1.75 * var(--unit));
--font-size-big: calc(2 * var(--unit));
--font-weight-thin: 300;
--font-weight-normal: 400;
--font-weight-bold: 500;
```css
--unit: 8px;
--padding: var(--unit);
--margin: var(--unit);
--border-radius: 3px;
```
They're intended to set consistent paddings and font-sizes across components, e.g.
```
They are intended to set consistent margins and paddings across components, e.g.
```css
.status {
padding-left: calc(var(--padding) * 2);
font-size: var(--font-size-small);
border-radius: var(--border-radius);
}
```
### Themable colors
After theme file gets parsed it provides list of theme-defined colors. Most of their values are different for light and dark themes. You can use them to preserve consitent view of extension with respect of selected theme.
## Themes
Lens is using two built-in themes defined in [the themes directory](https://github.com/lensapp/lens/tree/master/src/renderer/themes), one for light, and one for dark color schemes.
### Theme Variables
When Lens is loaded, it transforms the selected theme `json` file into a list of [CSS Custom Properties (CSS Variables)](https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties) which then gets injected into the `:root` element so any of the down-level components can use them.
![CSS vars listed in devtools](images/css-vars-in-devtools.png)
When the user changes the theme, the process is repeated, and new CSS Variables appear instead of previous ones.
If you want to follow a selected theme to keep the 'native' Lens look and feel, respecting the light/dark appearance of your extension, you can use the provided variables and build-in Lens components such as buttons, dropdowns, checkboxes etc.
There is a set of CSS Variables available for extensions to use for theming. They are all located inside `:root` and are defined in [app.scss](https://github.com/lensapp/lens/blob/master/src/renderer/components/app.scss):
```css
--font-main: 'Roboto', 'Helvetica', 'Arial', sans-serif;
--font-monospace: Lucida Console, Monaco, Consolas, monospace;
--font-size-small: calc(1.5 * var(--unit));
--font-size: calc(1.75 * var(--unit));
--font-size-big: calc(2 * var(--unit));
--font-weight-thin: 300;
--font-weight-normal: 400;
--font-weight-bold: 500;
```
"blue": "#3d90ce",
"magenta": "#c93dce",
"golden": "#ffc63d",
"halfGray": "#87909c80",
"primary": "#3d90ce",
"textColorPrimary": "#555555",
"textColorSecondary": "#51575d",
"textColorAccent": "#333333",
"borderColor": "#c9cfd3",
"borderFaintColor": "#dfdfdf",
"mainBackground": "#f1f1f1",
"contentColor": "#ffffff",
"layoutBackground": "#e8e8e8",
"layoutTabsBackground": "#f8f8f8",
"layoutTabsActiveColor": "#333333",
"layoutTabsLineColor": "#87909c80"
...
as well as in [the theme modules](https://github.com/lensapp/lens/tree/master/src/renderer/themes):
```
--blue: #3d90ce;
--magenta: #c93dce;
--golden: #ffc63d;
--halfGray: #87909c80;
--primary: #3d90ce;
--textColorPrimary: #555555;
--textColorSecondary: #51575d;
--textColorAccent: #333333;
--borderColor: #c9cfd3;
--borderFaintColor: #dfdfdf;
--mainBackground: #f1f1f1;
--contentColor: #ffffff;
--layoutBackground: #e8e8e8;
--layoutTabsBackground: #f8f8f8;
--layoutTabsActiveColor: #333333;
--layoutTabsLineColor: #87909c80;
...
```
They can be used in form of `var(--magenta)`.
They can be used in form of `var(--magenta)`, e.g.
```css
.status {
font-size: var(--font-size-small);
background-color: var(--colorSuccess);
}
```
A complete list of all themable colors can be found in the [color reference](../color-reference).
Colors values are located inside `src/renderer/themes/lens-dark.json` and `src/renderer/themes/lens-light.json` files.
### Theme switching
## Using CSS Variables inside CSS-in-JS components
If a developer uses an `Emotion` (or similar) framework to work with styles inside an extension, they can use variables in the following form:
When the light theme is active, the `<body>` element gets a "theme-light" class, `<body class="theme-light">`. If the class isn't there, assume the theme is dark. The active theme can be changed in the `Preferences` page:
![Color Theme](images/theme-selector.png)
Currently, there is no prescribed way of detecting changes to the theme in JavaScript. [This issue](https://github.com/lensapp/lens/issues/1336) hopes to improve on this. In the meantime, you can use a [MutationObserver](https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver) to observe the `<body>` element's `class` attribute to see if the "theme-light" class gets added to it:
```javascript
...
useEffect(function () {
const observer = new MutationObserver(function (mutations: MutationRecord[]) {
mutations.forEach((mutation: MutationRecord) => {
if (mutation.type === 'attributes' && mutation.attributeName === 'class') {
if ((mutation.target as HTMLElement).classList.contains('theme-light')) {
// theme is LIGHT
} else {
// theme is DARK
}
}
});
});
observer.observe(document.body, {
attributes: true,
attributeFilter: ['class'],
});
return function () {
observer.disconnect();
};
}, []); // run once on mount
...
```
## Injected styles
Every extention is affected by list of default global styles defined in [app.scss](https://github.com/lensapp/lens/blob/master/src/renderer/components/app.scss). These are basic browser resets and element styles like setting the `box-sizing` property for every element, default text and background colors, default font sizes, basic heading formatting, etc.
Extension may overwrite these if needed. They have low CSS specificity, so overriding them should be fairly easy.
## CSS-in-JS
If an extension uses a system like `Emotion` to work with styles, it can use CSS variables as follows:
```javascript
const Container = styled.div(() => ({
backgroundColor: 'var(--mainBackground)'
}));
```
```