This social card example uses an SVG background image to draw even more attention to it. The text has a highlighted gradient behind it to make it easy to read.
We run your HTML/CSS in a specialized instance of Google Chrome so that it renders exactly how you'd expect it to. Then we generate a screenshot from Chrome, crop it for you automatically and give you back a performance optimized URL to your image.
You can then use this URL anyway you'd like. You can download the image and host it somewhere else. Or directly use the URL in your apps and webpages.
We've spent years on this problem and our API generates millions of images each month. We continually improve it as people find new ways to use the API.