tab-size css property not working

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issues](https://copyq.readthedocs.io/en/latest/known-issues.html).
- OK

**Describe the bug**
TAB characters in the text that are copied to clipboard are rendered as 8 spaces by default. This behavior should be customizable using "tab-size" CSS property, but it doesn't work. None of the CSS settings in the theme.ini file works. Editing the items.css doesn't work either.

**To Reproduce**
1. Open Preferences and go to Appearance
2. Click Edit Theme button
3. Find the line which starts with **item_css=** and change it as;
```
item_css="
;tab-size:4"
```
4. Save and close the editor.
5. Click Apply button.

**Expected behavior**
Width of TABs should be 4 characters instead of 8

**Screenshots**
- none

**Version, OS and Environment**
- CopyQ 7.0.0
- Windows 10

**Additional context**
- none