[jackie_w]

Originally Posted by mxbndr

I'm wondering, is there documentation for how to target things in Kobo files?

If you want to examine the CSS streams in nickel you need @geek1011's cssextract executable (e.g. cssextract-windows.exe is the one for Windows). He used to distribute it in every release of kobopatch_xxx.zip but doesn't anymore. See here for more detail if you're interested. It may still on his GitHub website but I'm not sure exactly where it's stored. Once you've got it, all you do is pull out the nickel file from the relevant kobo firmware zip file and drop it onto the executable. It creates a single text file containing the CSS streams which you can examine at your leisure.

Originally Posted by mxbndr

For instance, I can infer from

  - FindZlib: "#row1col2"

that there is a grid with at least 2 columns, and from

      Replace: "#row1col2 {\n  qproperty-visible: false;\n}\n#row2 {\n  qproperty-visible: false;\n}"

The Home screen has a header (time and icons), a footer (4 Nav buttons) and between them is a 3x2 grid. What is in each "cell" can vary a bit, especially if you check the More>Beta Features>Large Print Mode box.
row1col1 & col2: Recent books
row2col1: MyBooks "tile" (recently duplicated in MyBooks navbutton)
row2col2: a variable "tile" usually showing books from one of your Collections or one of your Authors.
row3col1: link to Kobo store (recently duplicated in Discover navbutton)
row3col2: a random item from a select list of "useful (maybe) things". There are kobopatches to force this to something you might actually use.

Originally Posted by mxbndr

With that in mind, I'm also wondering what one patch would look like.

Try

Remove footer (row3) and My Books (row2) on home screen:
  - Enabled: yes
  - PatchGroup: Home screen visibility tweaks
  - FindZlib: "#row1col2"
  - ReplaceZlib:
      Find:    "#row1col2 {\n  qproperty-visible: false;\n}"
      Replace: "#row1col2 {\n  qproperty-visible: false;\n}\n#row2, #row3 {\n  qproperty-visible: false;\n}"

This is the whole contents for HomePageView.qss CSS resource in 4.25.15875 so you can get an idea what the existing Home screen patches are doing.:

Spoiler:

#mainContainer[qApp_deviceIsTrilogy=true] {
  qproperty-leftMargin: 32px;
}
#mainContainer[qApp_deviceIsPhoenix=true] {
  qproperty-leftMargin: 40px;
}
#mainContainer[qApp_deviceIsDragon=true] {
  qproperty-leftMargin: 57px;
}
#mainContainer[qApp_deviceIsStorm=true] {
  qproperty-leftMargin: 67px;
}
#mainContainer[qApp_deviceIsDaylight=true] {
  qproperty-leftMargin: 74px;
}
#mainContainer[qApp_deviceIsTrilogy=true] {
  qproperty-rightMargin: 32px;
}
#mainContainer[qApp_deviceIsPhoenix=true] {
  qproperty-rightMargin: 40px;
}
#mainContainer[qApp_deviceIsDragon=true] {
  qproperty-rightMargin: 57px;
}
#mainContainer[qApp_deviceIsStorm=true] {
  qproperty-rightMargin: 67px;
}
#mainContainer[qApp_deviceIsDaylight=true] {
  qproperty-rightMargin: 74px;
}
#mainContainer[qApp_deviceIsTrilogy=true] {
  qproperty-topMargin: 96;
  qproperty-spacing: 10;
}
#mainContainer[qApp_deviceIsPhoenix=true] {
  qproperty-topMargin: 126;
  qproperty-spacing: 14;
}
#mainContainer[qApp_deviceIsDragon=true] {
  qproperty-topMargin: 170;
  qproperty-spacing: 20;
}
#mainContainer[qApp_deviceIsStorm=true] {
  qproperty-topMargin: 192;
  qproperty-spacing: 23;
}
#mainContainer[qApp_deviceIsDaylight=true] {
  qproperty-topMargin: 220;
  qproperty-spacing: 26;
}
#row1[qApp_deviceIsTrilogy=true],
#row2[qApp_deviceIsTrilogy=true] {
  max-height: 280px;
  min-height: 280px;
}
#row1[qApp_deviceIsPhoenix=true],
#row2[qApp_deviceIsPhoenix=true] {
  max-height: 346px;
  min-height: 346px;
}
#row1[qApp_deviceIsDragon=true],
#row2[qApp_deviceIsDragon=true] {
  max-height: 488px;
  min-height: 488px;
}
#row1[qApp_deviceIsDaylight=true],
#row2[qApp_deviceIsDaylight=true] {
  max-height: 634px;
  min-height: 634px;
}
#row1[qApp_deviceIsStorm=true],
#row2[qApp_deviceIsStorm=true] {
  max-height: 556px;
  min-height: 556px;
}
[qApp_isFontScaleLarge=true] #row1[qApp_deviceIsTrilogy=true] {
  max-height: 392px;
  min-height: 392px;
}
[qApp_isFontScaleLarge=true] #row1[qApp_deviceIsPhoenix=true] {
  max-height: 484px;
  min-height: 484px;
}
[qApp_isFontScaleLarge=true] #row1[qApp_deviceIsDragon=true] {
  max-height: 683px;
  min-height: 683px;
}
[qApp_isFontScaleLarge=true] #row1[qApp_deviceIsDaylight=true] {
  max-height: 887px;
  min-height: 887px;
}
[qApp_isFontScaleLarge=true] #row1[qApp_deviceIsStorm=true] {
  max-height: 776px;
  min-height: 776px;
}
[qApp_isFontScaleLarge=true] #row2[qApp_deviceIsTrilogy=true] {
  max-height: 112px;
  min-height: 112px;
}
[qApp_isFontScaleLarge=true] #row2[qApp_deviceIsPhoenix=true] {
  max-height: 138px;
  min-height: 138px;
}
[qApp_isFontScaleLarge=true] #row2[qApp_deviceIsDragon=true] {
  max-height: 195px;
  min-height: 195px;
}
[qApp_isFontScaleLarge=true] #row2[qApp_deviceIsDaylight=true] {
  max-height: 253px;
  min-height: 253px;
}
[qApp_isFontScaleLarge=true] #row2[qApp_deviceIsStorm=true] {
  max-height: 220px;
  min-height: 220px;
}
[qApp_isFontScaleLarge=true] #row1col2 {
  qproperty-visible: false;
}