Text Selection Doesn't Align #20667

Drift that grows toward the bottom usually means the canvas and the text layer ended up different sizes. Easy to check in devtools:

document.querySelector('.canvasWrapper canvas').getBoundingClientRect()
document.querySelector('.textLayer').getBoundingClientRect()

If the canvas is a bit smaller, the usual suspect is a global box-sizing: border-box reset (Tailwind, Bootstrap and a lot of CSS resets have one). .pdfViewer .page has a 9px border, so with border-box the canvas loses 18px in each direction while the text layer keeps the full page size. With PDFSinglePageViewer at 100% that's a 798x1038 canvas under an 816x1056 text layer, and the selection drifts more the further down you go.

Putting the page back to content-box fixes it (checked with pdfjs-dist 6.3.289):

.pdfViewer .page {
  box-sizing: content-box;
}

If both rects are already the same size, it's something else, and a link to a repro would help.