This is cosmetic, but fairly annoying, particularly in the light theme variant of the GTK3 version (a bit less noticeable in the dark version): the tab widgets have a dark gray background, but this background does not extend to the right like normal GTK applications (or even other non-native apps like Firefox).
Please see the attached screenshot.
Steps to Reproduce:
1. Launch LibreOffice on a high-resolution, very wide-screen monitor, in light mode.
Tabs widgets background is not extended.
Tabs widgets background should fill the empty space.
User Profile Reset: No
Created attachment 189449 [details]
Pictured: LibreOffice writer (above) vs Firefox 117 (bottom-left) and the standard GTK4-demo application (bottom-right). Matching the GTK look would be ideal.
Are you using a Personalization theme?
Some similarity when the Personalization 'White' preinstalled theme while using the Light os/DE mode instead of the default look without theme.
Otherwise can not confirm an issue for Windows builds with defaults and Personalization not in use.
Version: 126.96.36.199.alpha0+ (X86_64) / LibreOffice Community
Build ID: d88779fc86385dde1215fd28b78a69eacc6b4f97
CPU threads: 8; OS: Windows 10.0 Build 19045; UI render: Skia/Vulkan; VCL: win
Locale: en-US (en_US); UI: en-US
No, I have no tweaks nor personalization going on. This is the default experience you get with the GTK version on Linux, whether from distro packages (such as from Fedora 38) or from the LibreOffice flatpak packages on Flathub (currently version 7.6). Many other users I've asked in public also experience this.
Thanks for the report, Jeff.
Which version of GNOME are you using?
Please also share the full info from Help > About LibreOffice.
This is running on GNOME 44 (eventually GNOME 45)
LibreOffice Community version: 188.8.131.52 (X86_64)
Build ID: 69edd8b8ebc41d00b4de3915dc82f8f0fc3b6265
CPU threads: 8; OS: Linux 6.4; UI render: default; VCL: gtk3
Locale: fr-CA (en_CA.UTF-8); UI: en-US
Note that this has affected every recent version of LibreOffice GTK3 I've seen in recent years, at least since the GTK3 port and the introduction of the Notebookbar, if I recall correctly.
Created attachment 189571 [details]
screenshot of effect of ca482cf39f25941040596e50d0e1ab7fa25dc1dd on border
(I've got an older GNOME version (3.36.8), probably why I can't reproduce.)
For me, the tab titles' background matches the rest of the space to their right. Since 7.5, there is a clearer delineation between the two, with a border drawn. Whereas in 7.4 and before, the whole length would look like one homogeneous block.
The change is from Caolán's ca482cf39f25941040596e50d0e1ab7fa25dc1dd, but looks like the issue you see is unrelated to that, seeing that you reproduced it with 7.4?
From your screenshot I see that you are running Ubuntu 20.04's patched up desktop environment, which is, strictly speaking, not really GNOME; as they have their own unofficial customizations, theming (which apparently does not use any background color for GTK notebook tab widgets), it does not represent GNOME's official UX and styling. And yeah, 3.36 is 3½ years old at this point, that's seven GNOME release cycles behind ;)
The "border" you see is the delimitations of where the tabs' background color would normally be rendered, so you are seeing the same thing as me, just that your theme doesn't render it properly... Workaround to reproduce: install the "GNOME Tweaks" tool and switch your GTK theme to "Adwaita", GNOME's official look.
Reproduced with 7.5.6 in Debian testing.