There is an option in the Expert Configuration to use a solid-fill for selected text instead of LibreOffice’s rectangle-with-border.
Here’s how you change to a solid selection background:
- From the menu bar, select Tools, Options… (default shortcut Alt-F12)
- Then from the list on the left select LibreOffice, Advanced
- Then press the Open Expert Configuration button
- In the new dialog that appears, type the word ‘Transparent’ in the slim text box and press Search
- A number of suggested results will appear. Look for ‘org.openoffice.Office.Common’, and there will be a match labelled ‘Drawinglayer’ - look to the right of this item and you will see ‘TransparentSelection boolean true’.
- Double click the word ‘true’ next to ‘boolean’ and it will change to ‘false’.
- Click OK to dismiss this dialog.
- Click OK to dismiss the Options dialog and return to your document.
You might need to restart Writer. For me, the changes took effect immediately:

If you’d like to change this option back to the outline style, repeat the steps and change ‘TransparentSelection boolean false’ back to ‘true’ by double clicking the word ‘false’.