This ensures that you're sending the smallest possible bundle to your users. When loading a page, the browser only blocks the first paint to retrieve the stylesheets that match the user's device (see Render-Blocking CSS).įinally, you'll want to minify your CSS to remove any extra whitespace or characters (see Minify CSS). Then add a media attribute to each stylesheet link. Then load the rest of the styles asynchronously using the preload link (see Defer unused CSS).Ĭonsider automating the process of extracting and inlining "Above the Fold" CSS using the Critical tool.Īnother approach to eliminating render-blocking styles is to split up those styles into different files, organized by media query. Similar to inlining code in a tag, inline critical styles required for the first paint inside a block at the head of the HTML page. # How to eliminate render-blocking stylesheets If there's code in a render-blocking URL that's not critical, you can keep it in the URL, and then mark the URL with async or defer attributes (see also Adding Interactivity with JavaScript).Ĭode that isn't being used at all should be removed (see Remove unused code). When the page loads, it will have what it needs to handle the page's core functionality. Once you've identified critical code, move that code from the render-blocking URL to an inline script tag in your HTML page. # How to eliminate render-blocking scripts Red (non-critical): Styles that apply to content not immediately visible code not being used in page's core functionality.Green (critical): Styles that are required for first paint code that's critical to the page's core functionality.Styles in CSS files and code in JavaScript files are marked in two colors: Click on a URL to inspect that file in the Sources panel. You can reduce the size of your pages by only shipping the code and styles that you need. When you load or run a page, the tab tells you how much code was used, versus how much was loaded: Chrome DevTools: Coverage tab. Use the Coverage tab in Chrome DevTools to identify non-critical CSS and JS. The first step towards reducing the impact of render-blocking resources is to identify what's critical and what's not. media="all" is considered render-blocking. Does not have a media attribute that matches the user's device specifically.When this attribute is present, the browser does not download the stylesheet. Lighthouse flags two types of render-blocking URLs: scripts and stylesheets. ![]() ![]() # Which URLs get flagged as render-blocking resources? The goal is to reduce the impact of these render-blocking URLs by inlining critical resources, deferring non-critical resources, and removing anything unused. The Opportunities section of your Lighthouse report lists all URLs blocking the first paint of your page.
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