FocusBlind от Swalter Factories

FocusBlind dims everything on the page except the paragraph your cursor is hovering over, forcing your brain to actually read instead of skim.
Move your cursor to any paragraph and the rest of the page fades into darkness. Move to the next paragraph and it follows. No setup, no accounts, one click to activate.
Features:

Works on any webpage — news articles, Wikipedia, research papers, blogs
Darkness slider — control how dim the background gets
Smooth transitions as you move between paragraphs
Adjustable transition speed
Your settings saved automatically between sessions
Lightweight — zero impact on page performance

Perfect for:

Students reading dense academic material
Researchers working through long documents
Anyone with ADHD or focus difficulties
Anyone who catches themselves skimming instead of actually reading

Note: FocusBlind works on standard webpages. It does not support Google Docs, which uses a canvas-based editor rather than standard HTML.
No accounts. No data collected. No internet connection needed. Everything runs locally in your browser.
One click. Total focus.