There is a size above which type stops behaving like text and starts behaving like structure. Somewhere past about eighty pixels, a headline is no longer something the reader reads word by word. It is a shape that organises the viewport, and it needs to be treated as one.
Tracking has to come down, and further than you think
Letter-spacing that looks correct at body size looks loose and amateurish at display size. Type designers space fonts for reading, which means for small sizes. At 300 pixels the gaps between letters are scaled up with everything else and become holes.
The correction is negative tracking, and the amount is larger than most people are comfortable with. A display headline wants somewhere between -0.04em and -0.09em depending on the typeface. Set it, then look at it from across the room. If the word still reads as a single object rather than a row of letters, it is close.
Line-height below one is not a mistake
At display scale, ascenders and descenders on adjacent lines can overlap slightly without colliding, because most lines do not have both. A line-height of 0.9 on a three-line headline pulls the block into a tight mass. At 1.4 — the value that is correct for body copy — the same headline falls apart into three separate bars of text with air between them.
Set it tight, then check the one line that has a descender above an ascender. That is the pair that decides how low you can go.
Measure is the rule that never changes
Everything above is about display type. The body text is the opposite problem: it wants a measure between roughly 45 and 75 characters, and that is true at every screen size and in every century of typesetting. A paragraph that runs the full width of a 1600-pixel viewport is unreadable no matter how good the typeface is, because the reader loses the line return.
The fix is a max-width in ch units on the prose container, not a media query. max-width: 68ch holds the measure whether the font is 16 or 19 pixels.
One editorial voice, used sparingly
The reason a serif italic inside a grotesque headline works is contrast, and contrast only functions when it is rare. One italic phrase per heading. Not two, and never a whole paragraph. The moment the exception becomes the pattern, the page loses the tension that made it feel considered.
