Header appearing different on homepage vs on template page

My header is appearing correctly on my homepage (https://kevin-lee.xyz/), with the left and right containers in one row. However, on the template page I created (https://kevin-lee.xyz/blog/), they are appearing stacked.

The containers are from generate blocks and have been set to:

• the container holding the two containers: display: flex (row, centre, centre); width: 100%;
• the two containers within are: display: flex; justify left, centre and right, centre. They each have a width of 45%.

Does anyone know why it displays correctly on my homepage but not the template page I created where I put a header up the top?

The page I need help with: [log in to see the link]