thefonts.sty

\RequirePackage{unicode-math}
\setmainfont[Numbers={OldStyle}]{STIXTwoText}[
    Extension={.otf},
    UprightFont={*-Regular},
    BoldFont={*-SemiBold},
    ItalicFont={*-Italic},
    BoldItalicFont={*-SemiBoldItalic}
]

\setsansfont{SourceSans3}[
    Path={/usr/local/share/fonts/SourceSans3/},
    Extension={.ttf},
    UprightFont={*-Regular},
    BoldFont={*-SemiBold},
    ItalicFont={*-Italic},
    BoldItalicFont={*-SemiBoldItalic}
]

\setmathfont{STIXTwoMath-Regular.otf}

\setmonofont{SourceCodePro}[
    Path={/usr/local/share/fonts/SourceCodePro/},
    UprightFont={*-Regular},
    BoldFont={*-SemiBold},
    ItalicFont={*-Italic},
    BoldItalicFont={*-SemiBoldItalic},
    Scale=0.9
]

% \setmathfont{STIX2Math.otf}[
%         SizeFeatures={
%             {Size=6-},
%             {Size=5-6,Font=STIX2Math.otf,Style=MathScript},
%             {Size= -5,Font=STIX2Math.otf,Style=MathScriptScript}
%         }]

%\newcommand{\blacksquare}{\mdlgblksquare}
%\newcommand{\square}{\mdlgwhtsquare}