[Bug] Fix colours for sidebar links in dark mode

[NdekoCode]

Improved colours for sidebar links in dark mode

In dark mode, the links in the sidebar are difficult to read:

• The contrast between the text and the background is low, making some elements difficult to read.
• Menu items that have been selected or hovered over are not sufficiently highlighted.

Expected correction

1. Increase the contrast between the text and the background to make the sidebar elements more legible.
2. Improve the highlighting of selected and hovered elements, so that they stand out better in dark mode.