The impedance design of the outer trace is the same as that of the 4 layers board.
The inner trace is generally more plane layer than the surface trace, and the electromagnetic environment is different from the surface.
The following is the third layer trace impedance control recommendation.
100 ohm differential impedance recommended design
line width, spacing 6/10/6mil.
The distance between the differential pair is ≥20mil (3W criterion).
90 ohm differential impedance recommended design
line width,line spacing 8/10/8mil.
The distance between the differential pair is ≥20mil (3W criterion).

Calculation parameters:
FR-4, thickness 1.6mm+/-10%, dielectric constant 4.4+/-0.2, copper thickness 1.0 oz (1.4mil), copper clad substrate(PP) 2116 (4.0-5.0mil), dielectric constant 4.3+/-0.2, solder mask thickness 0.6±0.2mil, dielectric constant 3.5+/-0.3.
Stack-up:
Silkscreen
Solder mask
Copper
Prepreg
Base material
Prepreg
Base material
Prepreg
Copper
Solder mask
Silkscreen