By appending just a few lines of HTML and CSS code, researcher Louis Dion-Marcil showed how an external sender could hide the very warning from an email message. Hiding "external sender" warning ...

Cascading style sheets (CSS) are browser instructions for styling HTML elements that can be added to Web pages in one of three ways: externally, internally or inline. Two advantages of using ...

2. HTML. We write HTML in files that end with the .html extension (like homepage.html).. To write HTML and CSS code, you’ll want to install a code editor.Nowadays, one of the most popular free ...

Web designers use CSS to turn basic HTML into cutting-edge visual layouts. ... By default, CSS code on an individual page overrides the CSS in an external .css file.

CSS instructions are added to HTML documents in order to style the document. These instructions are added within the tag. The tag must be placed within the head element of an HTML document.

Inline vs external styles. Furthermore, all HTML5 tags have a style property that one can use to override any style information defined at either the page style level or in an external style sheet.

And if everything else fails, you can even directly insert content from CSS by using base64-encoded data strings, although smuggling in encoded data would hardly count as “generating HTML”.

Your actual CSS classes will probably define other attributes such as font-family, border-style, margin or width. Override them using the same technique you used to make the DIV's background color ...