fix mat log overlaping nav

[StephDriver]

closes #4052

[StephDriver]

I'm closing this PR.

• The changes can't be made universally without clashing with custom css.
• There is no easy way to override them when they clash within the current structure without resorting to javascript.
• Where clashes occur, it is primarily because custom css has already been used to fix this issue in a way that is specific to that journal, and is not compatible with this general fix.

On discussion within the team, we decided that:

Material as a theme is near it's end of life, to long term solutions are not required. Therefore for now, we will provide this fix as a basic template for use in custom css as and when needed. But not alter the theme itself.