I’ve been using a fluid type and spacing system on the most recent builds I’ve completed. Here’s why I use it, and how I approach it. I mainly use SCSS (a Sass syntax), but it’s also very do-able with plain CSS.
The example above demonstrates the result on gortscott.com, resizing the window from about 2300px down to about 640px and back again. The type and spacing across the page begins scaling down when the window is 2095px wide and stops shrinking at 1047px wide. At that point the text begins to reflow as the CSS Grid layout continues to shrink. Eventually at 703px wide the layout shifts, and again at 543px wide.