PageSpeed: Put CSS in the document head
Overview
Moving inline style blocks and <link> elements from the document body to the document head improves rendering performance.
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Details from Google
Specifying external stylesheets and inline style blocks in the body of an HTML document can negatively affect the browser's rendering performance. Browsers block rendering a web page until all external stylesheets have been downloaded. Inline style blocks (specified with the <style> tag) can cause reflows and shifting of content. Therefore, it's important to put references to external stylesheets, as well as inline style blocks, in the head of the page. By ensuring that stylesheets are downloaded and parsed first, you can allow the browser to progressively render the page.