Most of what makes text comfortable to read is invisible when it works. You notice the failures — a line that runs too far, a heading that floats away from what it heads, a dark theme that turns crisp type into grey mush — and almost never the successes.

These are working notes. They are written down mainly so I stop re-deriving the same conclusions every time I start something new.

1. Measure and leading, and why 66 characters is a starting point rather than a rule Longer lines are not automatically worse. They need more room between them.
2. Optical alignment beats mathematical alignment The bounding box is a convenience for the layout engine, not for the eye.
3. Choosing a scale you can hold in your head Four sizes you remember will beat nine you have to look up.
4. A dark theme is not an inverted stylesheet Pure white on pure black is the one combination almost nobody should ship.