What does a red text-background mean in GitHub comparison view?

Question

I created a pull request and was browsing through, the differences are shown with light red/green line-brackgrounds, but some text is bolded with a red text background...

Answer 1

This is issue makes code review process hard especially for the React(JSX) projects. Almost all the files with JSX showed the red lines.

I fixed it by copy pasting

var errorLine = document.getElementsByClassName("pl-ii");
var i;
for (i = 0; i < errorLine.length; i++) {
    errorLine[i].style.backgroundColor = "transparent";
    errorLine[i].style.color = "#24292e";
}

on my console