Defining font size in standalone with xelatex

Question

I want to produce svg images of tikz pictures in a standalone environment that match the main document. So far everything works just fine. However, I am struggeling with defining the fontsize of the main document, which in this case is a beamer presentation with fontsize 9pt. How is it possible to set normalfontsize to 9pt in the standalone too?

MWE of main document:

\documentclass[9pt]{beamer}
\usepackage{fontspec}
\setmainfont{Arial}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}

\draw (-0.4,0) -- (10.6,0); 

\node[anchor=north east,align=right, inner sep=2mm, yshift=-0.5cm, xshift=0cm,font=\centering\bfseries\huge](a) at (current bounding box.east){This is the Main Title:};

\node[anchor=north east,align=right, inner sep=2mm, yshift=0.2cm, xshift=0cm,font=\centering\bfseries\large](b) at (a.south east){And this is the Subtitle that fits within the black border lines.};

\node[anchor=north east,align=right, inner sep=2mm, yshift=-0.4cm, xshift=0cm,font=\centering](c) at (b.south east){Name 1, Name 2};

\draw (-0.4,0) -- (-0.4,-5);
\draw (10.6,0) -- (10.6,4.5); 
\end{tikzpicture}

\end{document}

MWE of the Standalone:

\documentclass[crop,tikz,convert=pdf2svg]{standalone}
\usepackage[inkscapelatex=false]{svg}
\usepackage{fontspec}
\setmainfont{Arial}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}

\draw (-0.4,0) -- (10.6,0); 

\node[anchor=north east,align=right, inner sep=2mm, yshift=-0.5cm, xshift=0cm,font=\centering\bfseries\huge](a) at (current bounding box.east){This is the Main Title:};

\node[anchor=north east,align=right, inner sep=2mm, yshift=0.2cm, xshift=0cm,font=\centering\bfseries\large](b) at (a.south east){And this is the Subtitle that fits within the black border lines.};

\node[anchor=north east,align=right, inner sep=2mm, yshift=-0.4cm, xshift=0cm,font=\centering](c) at (b.south east){Name 1, Name 2};

\draw (-0.4,0) -- (-0.4,-5);
\draw (10.6,0) -- (10.6,4.5); 
\end{tikzpicture}

\end{document}

MWE of the standalone gives:

Answer 1

It is not clear what you like to get. I suspect that one from the following examples:

generated by:

\documentclass[margin=1mm,% added that border is better visible
                          % in real document you can delete margin
               tikz,convert=pdf2svg]{standalone}
%\documentclass[tikz, margin=1mm]{standalone}
\usetikzlibrary{fit,
                positioning}
\usepackage[inkscapelatex=false]{svg}
\usepackage{fontspec}
\setmainfont{Arial}

\begin{document}
    \begin{tikzpicture}[
node distance = 2mm and 0mm,
   box/.style = {inner sep=1mm, font=\bfseries#1, 
                 anchor=north east}
                        ]
\node[box=\huge](a) 
    {This is the Main Title:};
\node[box=\large, below left=of a.south east](b) 
    {And this is the Subtitle that fits within the black border lines.};
\node[box=\normalsize, below left=7mm and 0mm of b.south east](c) 
    {Name 1, Name 2};
%
\node[draw, inner sep=2mm, fit=(a) (b) (c)] {};
    \end{tikzpicture}
\end{document}

or

produced by:

\documentclass[margin=1mm,% added that border is better visible
                          % in real document you can delete margin
               tikz,convert=pdf2svg]{standalone}
%\documentclass[tikz, margin=1mm]{standalone}
\usetikzlibrary{fit,
                positioning}
\usepackage[inkscapelatex=false]{svg}
\usepackage{fontspec}
\setmainfont{Arial}

\begin{document}
    \begin{tikzpicture}[
node distance = 2mm and 0mm,
   box/.style = {inner sep=1mm, font=\bfseries#1}
                        ]
\node[box=\huge](a)  
    {This is the Main Title:};
\node[box=\large, below=of a](b) 
    {And this is the Subtitle that fits within the black border lines.};
\node[box=\normalsize, 
      below=7mm of b](c) 
    {Name 1, Name 2};
%
\node[draw, inner sep=2mm, fit=(a) (b) (c)] {};
    \end{tikzpicture}
\end{document}

Some comments about your MWE:

• by \documentclass[crop,tikz,convert=pdf2svg]{standalone} is loaded tikz package, therefore it is not needed to load it again with \usepackage{tikz}
• in nodes, which haven't defined text width the content of node is always in the middle of node, so defining align=... has no sense
• for font doesn't exist option \centering
• all nodes style definition differ only in used font size, consequently it is sensible to define common node shape style with free parameter which determine font size (by this code become more shorter and clear)
• it seems that (final) current bounding box is in time of its using unknown

Adddendum: The case, that you like to have this titles when are to long in more lines. This can be accomplished, with prescribing text width in node shape style options:

\documentclass[margin=1mm,% added that border is better visible
               tikz,convert=pdf2svg]{standalone}
\usetikzlibrary{fit,
                positioning}
\usepackage[inkscapelatex=false]{svg}
\usepackage{fontspec}
\setmainfont{Arial}

\begin{document}
    \begin{tikzpicture}[
node distance = 2mm and 0mm,
   box/.style = {text width=11cm, align=right, 
                 inner sep=1mm, font=\bfseries#1}
                        ]
\node[box=\huge](a)
    {This is the Main Title:};
\node[box=\large, below=of a](b)
    {And this is the Subtitle that fits within the black border lines.};
\node[box=\normalsize,
      below=7mm of b](c) 
    {Name 1, Name 2};
%
\node[draw, inner sep=2mm, fit=(a) (b) (c)] {};
    \end{tikzpicture}
\end{document}

or with centered text:

\documentclass[margin=1mm,% added that border is better visible
                          % in real document you can delete margin
               tikz,convert=pdf2svg]{standalone}
\usetikzlibrary{fit,
                positioning}
\usepackage[inkscapelatex=false]{svg}
\usepackage{fontspec}
\setmainfont{Arial}

\begin{document}
    \begin{tikzpicture}[
node distance = 2mm and 0mm,
   box/.style = {text width=11cm, align=center, 
                 inner sep=1mm, font=\bfseries#1}
                        ]
\node[box=\huge](a)
    {This is the Main Title:};
\node[box=\large, below=of a](b) 
    {And this is the Subtitle that fits within the black border lines.};
\node[box=\normalsize,
      below=7mm of b](c) 
    {Name 1, Name 2};
%
\node[draw, inner sep=2mm, fit=(a) (b) (c)] {};
    \end{tikzpicture}
\end{document}