When the vertical area under the toolbar or tabbed bar, in which the ruler is drawn, has the same color as the document area background - the tab indicator is rendered as a tiny black 'L' or line on top of, well, nothing. A user is likely not to recognize this as part of our UI - perhaps even think of this as some sort of glitch in a drawing/repainting function of the US or the app. Seeing this with: Version: 26.2.0.0.alpha0+ (X86_64) / LibreOffice Community Build ID: bc58a54d513702bc07906627dce073f05d7978fd CPU threads: 4; OS: Linux 6.12; UI render: default; VCL: gtk3 Locale: en-IL (en_IL); UI: en-US
That is at the left edge of the application frame v.aligned with the h.ruler on the document canvas it controls. Part of the Ruler object, hidden when the ruler is deactivated. Didn't check but maybe not icon based, rather a drawn button that takes the fg color assigned to ruler. https://help.libreoffice.org/25.8/en-US/text/shared/guide/tabs.html?&DbPAR=WRITER Apply an > 25.8 Appearance theme, e.g. "Dark Gray" or "Office 2003 Dark Blue" where the ruler bg differs from the application bg. Pretty obvious as the icon selector for the four tab types: Left tabs, Right tabs, Decimal tabs, Centered tabs.