Make training.bioconductor.org visually consistent with bioconductor.org

[mblue9]

Flagging suggestion of @lgatto raised in training group meeting 14th Oct 2024 (notes), we’d like to make training.bioconductor.org look more like bioconductor.org for consistency. This includes matching the top menu size and colour, as well as aligning the sidebar styling (similar to the layout at Bioconductor Books).

Notes:

• There isn’t an out-of-the-box template available so we’ll likely need to build this by combining components.
  Useful resources for this: bioconductor.org/layouts/components and bioconductor.org/assets/style.