@tsyum
I think it depends on what version you are using.

When I look under the tools menu>extensions manager I can install themes that change the overall look of the application... the toolbars for example. Link to the Extensions page below, Towards the bottom you'll see downloadable themes.

Related, as someone who prefers dark mode due to light sensitivity I've come to appreciate the option for a dark background on all documents when editing.

extensions.libreoffice.org/