/* Block diagrams carry explicit pixel width/height (injected by
   tools/book/generate.py from their viewBox) so <img> embeds have an
   intrinsic size. Scale them to the text column, keeping aspect ratio —
   without height:auto the pixel height attribute would win when max-width
   clamps the width, distorting wide graphs. */
.content img {
    max-width: 100%;
    height: auto;
}