TOC Rail, Body, Share Rail
The engineering-blog arrangement: orientation on the left, prose in the middle, actions on the right, all holding their places while the reader scrolls.
Create a three-region article layout: a left rail 240px wide holding a sticky table of contents that lists h2 anchors and highlights the current section with IntersectionObserver; a center prose column capped at 68 characters with 20px paragraph spacing, full-column code blocks on zinc-900, and scroll-margin-top of 96px on every heading; and a right rail with a sticky vertical share bar — three icon buttons plus copy-link with a two-second tooltip confirmation. Add a 3px indigo progress bar fixed under the header. After the body, render an author bio card and a related row of three same-category posts. Below xl, fold the TOC into a disclosure above the body and move the share buttons to a row at the end.