Created attachment 171082 [details]
Blue invoice template

Note: the confirming of this report is reserved for triagers in training, so if you are a veteran, please skip :)

1. Open attached XLTX template
2. Compare with the attached PDF

Notice that the gray cell backgrounds in the Item Description / Amount section are missing.

Examining the styles.xml we see

<tableStyles count="1" defaultTableStyle="TableStyleMedium2" defaultPivotStyle="PivotStyleLight16">
    <tableStyle name="Business Table" pivot="0" count="3" xr9:uid="{00000000-0011-0000-FFFF-FFFF00000000}">
        <tableStyleElement type="wholeTable" dxfId="6"/>
        <tableStyleElement type="headerRow" dxfId="5"/>
        <tableStyleElement type="secondRowStripe" dxfId="4"/>
    </tableStyle>
</tableStyles>

Explanation: dxfId (Formatting Id) 	Zero-based index to a dxf record in the dxfs collection, specifying differential formatting to use with this Table or PivotTable style element.
https://docs.microsoft.com/en-us/dotnet/api/documentformat.openxml.spreadsheet.tablestyleelement?view=openxml-2.8.1

So our gray cell style should be secondRowStripe. It points to the dxf with the zero-based index of 4. Thus, in styles.xml we find it inside the <dxfs count="7"> element as

<dxf>
    <fill>
        <patternFill>
            <bgColor theme="0" tint="-4.9989318521683403E-2"/>
        </patternFill>
    </fill>
</dxf>

Note: other issues in the same template are already reported. Missing borders is bug 141588 while missing gradient background depends on bug 49177.

Arch Linux 64-bit
Version: 7.2.0.0.alpha0+ / LibreOffice Community
Build ID: 3b6408988487c886adc5415f7050f9da13d2e16b
CPU threads: 8; OS: Linux 5.11; UI render: default; VCL: kf5
Locale: fi-FI (fi_FI.UTF-8); UI: en-US
Calc: threaded
Built on 8 April 2021