Broken monospace without custom font

In codeblocks, custom font is required not only for look but for correct rendering.

1. Special characters like boxing chars and special font glyphs

<img width="552" height="80" alt="image" src=" />

2. Incorrect glyph alignment from font fallbacks

A CJK glyph should be double-width but mixing glyph from different fonts break this alignment.

"SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace

"a" is rendered from "Liberation Mono" and "가" is rendered from "monospace" which has a different size.

• Liberation Mono: 'a' is 10px wide
• monospace: 'a' is 8px wide, '가' is 16px wide (1:2)
• 10px:16px is not 1:2 anymore