Is it the hunk header you're referring to? That's something that git outputs, like this, before the diff hunk: @@ -62,17 +62,17 @@ class MyClass: Delta make

Is it the hunk header you're referring to? That's something that git outputs, like this, before the diff hunk: @@ -62,17 +62,17 @@ class MyClass: Delta makes that more prominent by surrounding it with a box (by default) and getting rid of the for-machines characters that git puts there. It doesn't apply background colors to it though: delta only applies background red and green shading to removed/added lines. (I believe that one can customize the regular expressions that git uses to decide on the hunk header; they're sometimes appropriate and sometimes not, for the languages that I use.)