Make "Title4" more different from the "bold text"

**Is your feature request related to a problem? Please describe.**
It is hard to distinguish "H4 title" and the "bold text". Because their font-size and font-weight is merely different. So it's less clear to know the paragraph level when using "H4 title".

**Describe the solution you'd like**

I hope the "H4 title" can be more different from the "bold text" , remains the features as a title.

**Describe alternatives you've considered**

- Solution 1: Make the font-size of "H4 title" larger than the "bold text".
- Solution 2: Make the color of "H4 title" deep gray. Therefore the font-size need not to be changed.

**Thank you**