In this article, the author explains why 16 pixels should generally be the minimum size for body copy in modern Web design.| Smashing Magazine
In the beginning there was NCSA Mosaic, and Mosaic called itself NCSA_Mosaic/2.0 (Windows 3.1), and Mosaic displayed pictures along with text, and there was much rejoicing.| webaim.org
The grid CSS property is a shorthand property that sets all of the explicit and implicit grid properties in a single declaration.| developer.mozilla.org
Download Stylus for Firefox. Redesign your favorite websites with Stylus, an actively developed and community driven userstyles manager. Easily install custom themes from popular online repositories, or create, edit, and manage your own personalized CSS stylesheets.| addons.mozilla.org
The :is() CSS pseudo-class function takes a selector list as its argument, and selects any element that can be selected by one of the selectors in that list. This is useful for writing large selectors in a more compact form.| MDN Web Docs
The :not() CSS pseudo-class represents elements that do not match a list of selectors. Since it prevents specific items from being selected, it is known as the negation pseudo-class.| MDN Web Docs
The functional :has() CSS pseudo-class represents an element if any of the relative selectors that are passed as an argument match at least one element when anchored against this element. This pseudo-class presents a way of selecting a parent element or a previous sibling element with respect to a reference element by taking a relative selector list as an argument.| MDN Web Docs
This will do you fine these days (IE 8 and up):| CSS-Tricks
The @media CSS at-rule can be used to apply part of a style sheet based on the result of one or more media queries. With it, you specify a media query and a block of CSS to apply to the document if and only if the media query matches the device on which the content is being used.| MDN Web Docs
The clip-path CSS property creates a clipping region that sets what part of an element should be shown. Parts that are inside the region are shown, while those outside are hidden.| MDN Web Docs
The border-radius CSS property rounds the corners of an element's outer border edge. You can set a single radius to make circular corners, or two radii to make elliptical corners.| MDN Web Docs
The background-size CSS property sets the size of the element's background image. The image can be left to its natural size, stretched, or constrained to fit the available space.| MDN Web Docs
Download uMatrix for Firefox. Point & click to forbid/allow any class of requests made by your browser. Use it to block scripts, iframes, ads, facebook, etc.| addons.mozilla.org
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The web home of Eric A. Meyer, CSS guy; and his wife Kathryn, doctor of nursing.| meyerweb.com