I suggest you choose Hierarchical
from the bottom menu is the styles side pane. In this view, you see the inheritance chain between styles.
Draw is less organised style-wise than Writer. One of the problem is there are 3 roots for styles (contrary to Writer where Default Paragraph Style is the ancestor of all styles): Default Drawing Style, Graphic and Text.
Dimension lines are styled Arrow Line which inherit from Lines which inherit from Graphic.
Therefore, customising Default Drawing Style (default for shapes) has no effect on dimension lines.
Customise Arrow Line to fix the issue.
To show the community your question has been answered, click the ✓ next to the correct answer, and “upvote” by clicking on the ^ arrow of any helpful answers. These are the mechanisms for communicating the quality of the Q&A on this site. Thanks!
In case you need clarification, edit your question (not an answer which is reserved for solutions) or comment the relevant answer.