Greenlet is a highly performant theme by default. However, it also provides the option to change the performance settings based on the user preference.
Access performance settings
To access performance settings navigate to Appearance > Customize > Performance
Inline CSS and Javascript
In performance settings, you can inline and defer CSS and Javascript files. Inlining styles or scripts will save extra network requests made by your site visitors’ browser. We recommend enabling this option if your site does not contain a lot of other plugins, or a dedicated performance plugin like Autoptimize. However, if you are using a performance plugin we suggest to inline only “Above the fold” styles and scripts using the plugin to save a large initial payload.
Defer CSS
Defer CSS option allows the styles to load after the page load. This enables the browsers to render the content first and then load the styles so that rendering is not blocked when parsing the styles. Please note that enabling this option will let the browser to render the content without any styles first (hence users can notice the same) and then apply styles once the stylesheet is loaded.