Hope slightly increase the font-size of the code block

[devlzl]

When I use BlockSuite alone, the font-size of the code block is 14px, which I think is fine; But in app.affine.pro, the font-size of the code block is only 12px, which I think is a bit small on non-high-resolution screens. When I used affine to write articles and add code blocks on my old macbook air, I felt a little bit of pain.