From cf081ce55ddc35d09dfae9ac53ab7cfa80cf660b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aliz=C3=A9=20Debray?=
 <33580481+alizedebray@users.noreply.github.com>
Date: Thu, 11 Jul 2024 11:37:54 +0200
Subject: [PATCH] feat(internet-header): expose CSS custom properties (#3200)

Co-authored-by: Philipp Gfeller <1659006+gfellerph@users.noreply.github.com>
---
 .changeset/flat-gifts-report.md               |  6 ++++
 .../.storybook/styles/preview.scss            |  1 +
 .../header-css-variables.docs.mdx             | 17 ++++++++++
 .../header-css-variables.stories.ts           | 32 +++++++++++++++++++
 .../internet-header/internet-header.docs.mdx  | 22 +++++++++++--
 packages/internet-header/package.json         |  2 +-
 .../post-internet-header.scss                 | 17 ++++------
 .../post-internet-header.tsx                  |  6 ++++
 packages/internet-header/src/root.scss        |  8 +++++
 .../internet-header/src/utils/mixins.scss     | 32 +++++++++++++++++++
 .../internet-header/src/utils/variables.scss  | 21 ++++++++++++
 .../internet-header/stencil.config.dev.ts     | 13 ++++++++
 packages/internet-header/stencil.config.ts    |  2 +-
 13 files changed, 164 insertions(+), 15 deletions(-)
 create mode 100644 .changeset/flat-gifts-report.md
 create mode 100644 packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.docs.mdx
 create mode 100644 packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.stories.ts
 create mode 100644 packages/internet-header/src/root.scss
 create mode 100644 packages/internet-header/src/utils/variables.scss
 create mode 100644 packages/internet-header/stencil.config.dev.ts

diff --git a/.changeset/flat-gifts-report.md b/.changeset/flat-gifts-report.md
new file mode 100644
index 0000000000..266c7f488b
--- /dev/null
+++ b/.changeset/flat-gifts-report.md
@@ -0,0 +1,6 @@
+---
+'@swisspost/internet-header': minor
+'@swisspost/design-system-documentation': minor
+---
+
+Added a new stylesheet containing `:root` CSS custom properties to facilitate implementing styles relative to the header. This will allow putting sticky content right below the header.
diff --git a/packages/documentation/.storybook/styles/preview.scss b/packages/documentation/.storybook/styles/preview.scss
index 1b2cf39544..5eaa9141e8 100644
--- a/packages/documentation/.storybook/styles/preview.scss
+++ b/packages/documentation/.storybook/styles/preview.scss
@@ -3,6 +3,7 @@
 @use '@swisspost/design-system-styles/intranet.scss';
 @use '@swisspost/design-system-styles/core.scss' as post;
 @use '@swisspost/design-system-styles/mixins/utilities';
+@use '@swisspost/internet-header/dist/swisspost-internet-header/swisspost-internet-header.css';
 @use './components';
 
 #storybook-root,
diff --git a/packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.docs.mdx b/packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.docs.mdx
new file mode 100644
index 0000000000..a93f37dfbe
--- /dev/null
+++ b/packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.docs.mdx
@@ -0,0 +1,17 @@
+import { Meta, Canvas, Controls } from '@storybook/blocks';
+import * as HeaderStories from './header-css-variables.stories';
+import '../header.scss';
+
+<Meta of={HeaderStories} />
+
+<div className="container">
+  <h1>Internet Header CSS Variables</h1>
+  <p className="lead">When you need to implement styling relative to the header.</p>
+</div>
+
+<Canvas sourceState='shown' of={HeaderStories.Default} />
+
+## Style Imports
+
+To access the CSS variables for the header, you need to install an optional stylesheet into your project.
+Learn more in the <a href="/?path=/docs/cfa21cbc-5f8d-4a42-8165-7f6ed20bf133--docs#css-variables">header CSS variables stylesheet documentation</a>.
diff --git a/packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.stories.ts b/packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.stories.ts
new file mode 100644
index 0000000000..7bb135c8e2
--- /dev/null
+++ b/packages/documentation/src/stories/components/internet-header/header/overrides-stories/header-css-variables.stories.ts
@@ -0,0 +1,32 @@
+import meta from '@/stories/components/internet-header/header/header.stories';
+import * as HeaderStories from '@/stories/components/internet-header/header/header.stories';
+import { Args } from '@storybook/web-components';
+import { html } from 'lit';
+
+export default {
+  ...HeaderStories.default,
+  id: 'bfdf4e7c-37d3-40f8-a5d0-734f3e6612b5',
+  title: 'Components/Internet Header/Header/CSS Variables',
+};
+
+export const Default = {
+  render: (args: Args, context: any) => {
+    return html`
+      <style>
+        #my-div {
+          z-index: 1000;
+          top: 0;
+          transition: var(--post-header-slide-in-transition);
+        }
+
+        swisspost-internet-header.scrolling-up + #my-div {
+          top: var(--post-header-height);
+        }
+      </style>
+      ${meta.render && meta.render(args, context)}
+      <p id="my-div" class="position-sticky bg-nightblue p-regular">
+        I am sticky! I am always positioned right below the header when you scroll up and down.
+      </p>
+    `;
+  },
+};
diff --git a/packages/documentation/src/stories/getting-started/packages/internet-header/internet-header.docs.mdx b/packages/documentation/src/stories/getting-started/packages/internet-header/internet-header.docs.mdx
index 01df1a5d20..2639b1b6fb 100644
--- a/packages/documentation/src/stories/getting-started/packages/internet-header/internet-header.docs.mdx
+++ b/packages/documentation/src/stories/getting-started/packages/internet-header/internet-header.docs.mdx
@@ -21,9 +21,11 @@ import { SourceDarkMode } from '@/../.storybook/preview';
 The header for client-facing applications.
 
 <ul>
-  <li><a href="#configuration" target="_self">Configuration</a></li>
+  <li><a href="#preparation" target="_self">Preparation</a></li>
   <li><a href="#installation" target="_self">Installation</a></li>
-  <li><a href="#migration-from-the-old-header" target="_self">Migration Guide</a></li>
+  <li><a href="#css-variables" target="_self">CSS Variables</a></li>
+  <li><a href="#usage-with-angular" target="_self">Usage with Angular</a></li>
+  <li><a href="#migration-from-the-old-header" target="_self">Migration from the old header</a></li>
 </ul>
 
 ## Preparation
@@ -99,6 +101,22 @@ Available CDNs:
   </PostTabPanel>
 </PostTabs>
 
+## CSS Variables
+
+The internet header package provides a stylesheet aimed at facilitating the use of key CSS variables beyond the header itself.
+This stylesheet allows you to access CSS variables to implement styling relative to the header as needed, but it is completely optional.
+
+<PostTabs>
+  <PostTabHeader slot="tabs" panel="sass-import">Sass Import</PostTabHeader>
+  <PostTabPanel name="sass-import">
+    <Source code={`@use "@swisspost/internet-header/dist/siwsspost-internet-header/siwsspost-internet-header.css";`} dark={SourceDarkMode} language="scss" />
+  </PostTabPanel>
+  <PostTabHeader slot="tabs" panel="html-import">HTML Import</PostTabHeader>
+  <PostTabPanel name="html-import">
+    <Source code={`<link rel="stylesheet" href="@swisspost/internet-header/dist/siwsspost-internet-header/siwsspost-internet-header.css"/>`} dark={SourceDarkMode} language="html" />
+  </PostTabPanel>
+</PostTabs>
+
 ## Usage with Angular
 
 For Angular user, please have a look at [How to integrate Web Components inside Angular](/?path=/docs/8426deb2-3d6d-4fcc-90e6-1ca9737b2ed0--docs#usage-of-web-components)
diff --git a/packages/internet-header/package.json b/packages/internet-header/package.json
index 8368897950..c0b5beea10 100644
--- a/packages/internet-header/package.json
+++ b/packages/internet-header/package.json
@@ -27,7 +27,7 @@
     "loader/"
   ],
   "scripts": {
-    "dev": "stencil build --serve --port 9310 --watch --docs-readme --dev",
+    "dev": "stencil build --serve --port 9310 --watch --docs-readme --dev --config stencil.config.dev.ts",
     "start": "stencil build --watch --docs-readme",
     "build": "stencil build --docs-readme",
     "clean": "rimraf www dist loader",
diff --git a/packages/internet-header/src/components/post-internet-header/post-internet-header.scss b/packages/internet-header/src/components/post-internet-header/post-internet-header.scss
index beed680f81..6c32f688e2 100644
--- a/packages/internet-header/src/components/post-internet-header/post-internet-header.scss
+++ b/packages/internet-header/src/components/post-internet-header/post-internet-header.scss
@@ -2,6 +2,7 @@
 @use '@swisspost/design-system-styles/placeholders/color' as color-ph;
 @use '../../utils/utils.scss';
 @use '../../utils/mixins.scss';
+@use '../../utils/variables.scss';
 @use './logo-animation/logo-animation.scss';
 
 :host {
@@ -13,18 +14,10 @@
   font-weight: 300;
   z-index: var(--header-z-index, 10);
 
-  --header-height: 3.5rem; // 56px
-  --meta-header-height: 0px; // Not visible on mobile
   --language-dropdown-margin-top: 0px;
 
-  @include mixins.min(lg) {
-    --meta-header-height: 3rem; // 48px
-    --header-height: 4rem; // 64px
-  }
-
-  @include mixins.min(xl) {
-    --header-height: 4.5rem; // 72px
-  }
+  @include mixins.set-custom-property(--meta-header-height, variables.$meta-header-height);
+  @include mixins.set-custom-property(--header-height, variables.$header-height);
 }
 
 // Set height to 0 if meta is never visible
@@ -62,7 +55,9 @@
   :host(.stickyness-minimal.scrolling-up),
   :host(.stickyness-minimal.dropdown-open) {
     top: calc(var(--meta-header-height, 0px) * -1);
-    transition: top 200ms ease-out;
+
+    @include mixins.set-custom-property(--header-slide-in-transition, variables.$header-slide-in-transition);
+    transition: var(--header-slide-in-transition);
   }
 }
 
diff --git a/packages/internet-header/src/components/post-internet-header/post-internet-header.tsx b/packages/internet-header/src/components/post-internet-header/post-internet-header.tsx
index c1b2b84af9..a55d3fced6 100644
--- a/packages/internet-header/src/components/post-internet-header/post-internet-header.tsx
+++ b/packages/internet-header/src/components/post-internet-header/post-internet-header.tsx
@@ -223,6 +223,12 @@ export class PostInternetHeader {
       this.host.classList.add('header-loaded');
       if (this.meta && this.metaNav) {
         this.updateLogoAnimation = registerLogoAnimationObserver(this.metaNav, this.host);
+      } else {
+        // Set height to 0 if meta is never visible and global variables are defined
+        const rootStyles = window.getComputedStyle(document.documentElement);
+        if (rootStyles.getPropertyValue('--post-meta-header-height') !== '') {
+          document.documentElement.style.setProperty('--post-meta-header-height', '0px');
+        }
       }
     });
 
diff --git a/packages/internet-header/src/root.scss b/packages/internet-header/src/root.scss
new file mode 100644
index 0000000000..80d0448b48
--- /dev/null
+++ b/packages/internet-header/src/root.scss
@@ -0,0 +1,8 @@
+@use 'utils/mixins';
+@use 'utils/variables';
+
+:root {
+  @include mixins.set-custom-property(--post-meta-header-height, variables.$meta-header-height);
+  @include mixins.set-custom-property(--post-header-height, variables.$header-height);
+  @include mixins.set-custom-property(--post-header-slide-in-transition, variables.$header-slide-in-transition);
+}
diff --git a/packages/internet-header/src/utils/mixins.scss b/packages/internet-header/src/utils/mixins.scss
index bae29f2bc2..68d4ca39ae 100644
--- a/packages/internet-header/src/utils/mixins.scss
+++ b/packages/internet-header/src/utils/mixins.scss
@@ -1,4 +1,6 @@
 @use "sass:map";
+@use 'sass:selector';
+@use 'sass:string';
 @use "@swisspost/design-system-styles/variables/breakpoints";
 
 @mixin min($point) {
@@ -45,3 +47,33 @@
     padding-left: 40px;
   }
 }
+
+@mixin set-custom-property($var, $value) {
+  @if (type-of($value) == 'map') {
+    @include _responsive-custom-property($var, $value);
+  } @else {
+    @include _custom-property($var, $value);
+  }
+}
+
+@mixin _responsive-custom-property($var, $values) {
+  $previous-value: null;
+  @each $breakpoint, $value in $values {
+    @if($value == $previous-value) {
+      // no styles
+    } @else if($breakpoint == xs) {
+      @include _custom-property($var, $value);
+    } @else {
+      @include min($breakpoint) {
+        @include _custom-property($var, $value);
+      }
+    }
+
+    $previous-value: $value;
+  }
+}
+
+@mixin _custom-property($var, $value) {
+  $is-root: selector.is-superselector(&, ':root');
+  #{$var}: if($is-root, $value, var(#{string.insert($var, "post-", 3)}, $value));
+}
diff --git a/packages/internet-header/src/utils/variables.scss b/packages/internet-header/src/utils/variables.scss
new file mode 100644
index 0000000000..c54317dc2d
--- /dev/null
+++ b/packages/internet-header/src/utils/variables.scss
@@ -0,0 +1,21 @@
+$meta-header-height: (
+  xs: 0px,
+  sm: 0px,
+  rg: 0px,
+  md: 0px,
+  lg: 3rem,
+  xl: 3rem,
+  xxl: 3rem,
+);
+
+$header-height: (
+  xs: 3.5rem,
+  sm: 3.5rem,
+  rg: 3.5rem,
+  md: 3.5rem,
+  lg: 4rem,
+  xl: 4.5rem,
+  xxl: 4.5rem,
+);
+
+$header-slide-in-transition: top 200ms ease-out;
diff --git a/packages/internet-header/stencil.config.dev.ts b/packages/internet-header/stencil.config.dev.ts
new file mode 100644
index 0000000000..7c3a2205a8
--- /dev/null
+++ b/packages/internet-header/stencil.config.dev.ts
@@ -0,0 +1,13 @@
+import { Config } from '@stencil/core';
+import { sass } from '@stencil/sass';
+import { config as prodConfig } from './stencil.config';
+
+export const config: Config = {
+  ...prodConfig,
+  globalStyle: 'src/styles.scss',
+  plugins: [
+    sass({
+      includePaths: ['node_modules'],
+    }),
+  ],
+};
diff --git a/packages/internet-header/stencil.config.ts b/packages/internet-header/stencil.config.ts
index a2a32d5e43..ad811cdbb2 100644
--- a/packages/internet-header/stencil.config.ts
+++ b/packages/internet-header/stencil.config.ts
@@ -4,7 +4,7 @@ import scss from 'rollup-plugin-scss';
 
 export const config: Config = {
   namespace: 'swisspost-internet-header',
-  globalStyle: 'src/styles.scss',
+  globalStyle: 'src/root.scss',
   buildEs5: 'prod',
   sourceMap: false,
   bundles: [