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    Customising your AMP sub-theme

    Now that you’ve set up AMP and created a sub-theme, you’ll need to create CSS to style your pages. In this guide, we'll cover the following topics:

    Limitations

    AMP (Accelerated Mobile Pages) are a stripped down form of HTML, designed to be lightweight and serve mobile content much faster than regular pages. Naturally, this creates limitations to ensure fast delivery of content.

    No Javascript

    Custom JS and additional libraries can add a lot of weight to page load times, so AMP pages do not support these.

    CSS size

    Your AMP sub-theme CSS styles (which are actually held in a Drupal html.twig file) cannot exceed 75kb.

    See recommended approach to CSS for more info.

    Disallowed CSS

    See the Disallowed styles section on the amp.dev website for latest information.

    Custom fonts

    Any imported fonts you’ve specified in Acquia Cohesion > Website settings > Font libraries will be available to your AMP sub-theme to use in CSS.

    The following origins are whitelisted by AMP:

    Uploaded font packages will not work unless you create @font-face declarations for these fonts in your sub-theme CSS file. These can be copied from the sites/default/files/cohesion/styles/base/stylesheet.min.css file.

    This also applies to icon fonts specified in Acquia Cohesion > Website settings > Icon libraries.

    Make sure that any custom font you use is as lightweight as possible, as this will impact page load time.

    Useful modules

    Module Description
    Field Formatter Class Allows classes to be added to the outer wrapper of any Drupal field display, which provides more control for theming.
    Title Field for Manage Display Creates a Title field in content types that shows up in the Manage display tab. Allows more control over page title placement.
    Breadcrumb Extra Field Creates a Breadcrumb field in content types that shows up in the Manage display tab. Allows more control over breadcrumb placement.
    Context (and Context UI submodule) In combination with context visibility settings on Acquia Cohesion elements, you can create AMP-alternative content. E.g. replacing Picture with Image.

    Identifying content for AMP optimisation

    Initially your AMP pages will look very different to regular pages as no styles will be applied - these have to be generated manually.

    We recommend you identify a content type that is most likely to benefit from AMP optimisation (eg. blog) as a starting point. You can then expand to other content types as necessary, providing you do not exceed the 50kb CSS limit.

    Block and content type optimisation

    Once you’ve identified a content type to work with, you may need to reorganise your block and content type field placement to provide the best user experience. Acquia Cohesion templated content (master templates, content templates etc) are not supported with AMP themes.

    Select the correct tab before making changes to block or content type field layout, so that other displays are unaffected. For blocks this is your sub-theme, for content types it will be AMP.

    Make sure any fields on your content type are using the correct formatter. For example, Image needs to be changed to AMP Image.

    See the useful modules section for some community modules that will help with this process.

    Recommended approach to CSS

    To keep your theme CSS as light as possible, we recommend using a CSS preprocessor such as SCSS. By setting the SCSS output style to compressed, it will minify the CSS into a single line and provide room for extra CSS.

    Best practice

    • Keep CSS selectors as short as possible - single-level element (e.g. H1) or class (e.g. .myclass) selectors are ideal.

    • Never use ID selectors (e.g. #myid) as these are much harder to override.

    • If multi-level selectors are necessary, limit to no more than three levels (e.g. ul li a) - if possible add classes to these elements to give more control.

    • Don’t use an autoprefixer - whilst this is normally recommended for legacy browser support, AMP is a modern development framework that targets mobile devices that don’t require autoprefixing. It will also reduce the amount of CSS generated.

    • Keep it simple - your AMP pages won’t always look the same as your regular pages, given that page load speed is the priority.

    CSS structure

    Whilst the CSS you define for your AMP sub-theme will differ from project to project, we recommend using the following outline.

    CSS section Description
    @font-face declarations Always put your font declarations first, so that you can specify font-family settings for any following selectors.
    Acquia Cohesion grid styles As no external styles are loaded, you will need to duplicate Acquia Cohesion’s grid CSS to implement a responsive layout. These include coh-row, coh-row-inner, coh-column and coh-col-* classes and associated styles.
    Acquia Cohesion base styles Some styles that you’ve defined through Acquia Cohesion base styles may need duplicating. For example heading, list and paragraph styles.
    Drupal core styles you may need to duplicate some of Drupal's core CSS. Examples include hidden, visually-hidden, focusable and invisible.
    Drupal element styles CSS that targets Drupal elements, blocks or fields. This would include styles for any custom classes you’ve added to content type fields.
    Acquia Cohesion custom styles Some styles that you’ve defined through Acquia Cohesion custom styles may need duplicating.
    Acquia Cohesion inline element styles Styles that you’ve applied directly to Acquia Cohesion elements through the Styles tab.

    Useful resources

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