This isn’t actually a Pluto issue, it’s just a clash between Julia’s string interpolation using a single $ and inserting LaTeX into markdown with paired $$. Usually, a bunch of characters without spaces between $$ will be interpreted as LaTeX, e.g. the $C(max)$ at the end of your string (although the actual rules for what gets interpreted as what are not super straightforward).
Actually, the syntax highlighting here is also giving you a hint that the last $ at the end is not needed. If you remove it, it renders correctly:
begin
Cmin=10.0; Cmax=200.;
Cslider = @bind SlideValC Slider(Cmin:0.1:Cmax, default=51);
md" $(Cmin) J/m^2/K $(Cslider) $(Cmax)"
end
![]()