Gridman is a CSS Grid inspector for Chrome
CSS-grid highlighter. that is lightning Fast! - activates on grid mouseover
• display: grid
• Nested grids support !
*** You are trying it towards local file like 'file:///...' - but nothing shows up
Gridman , like any chrome extension, will not work on local files. Chrome is not allowing it due to security reasons. And it is correct. You can imagine implications if any chrome extension would be able to access file system on your computer.
To use Gridman on local files i'd recommend a tiny http-server which you can get here https://www.npmjs.com/package/http-server