Reduce the size fo a tikz picture

Question

I have a flowchart created using tikz.

Example,

\documentclass[tikz, margin=3mm]{standalone}
\usetikzlibrary{backgrounds,
                fit,
                positioning}

\begin{document} 
    \begin{tikzpicture}[
 node distance = 4mm and 4mm,
   base/.style = {rectangle, draw, align=center}, 
  steps/.style = {base, rounded corners, fill=gray!50, 
                  minimum height=1cm, text width=3cm},
process/.style = {base,
                  minimum height=2cm, text width=4cm, fill=white}
                  ]
\node (process1) [process]                      {text text};
\node (process2) [process, right=of process1]   {text text
    text text text text text text text text text text text text text text text text};
\node (process3) [process, right=of process2]   {text text text};
\node (step1) [steps, above=of process1]                   {Step 1};
\node (step2) [steps, above=of process2]   {Step 2};
\node (step3) [steps, above=of process3]   {Step 3};
%
\scoped[on background layer]
{
\node[fit=(step1) (process1), fill=red!20] {};
\node[fit=(step2) (process2), fill=red!40] {};
\node[fit=(step3) (process3), fill=red!60] {};
}
    \end{tikzpicture}
\end{document}

Could someone please let me know how the size of the figure created within \begin{tikzpicture}..\end{tikzpicture} can be reduced to 0.8 of its original size?

EDIT:
I tried scale=0.8 and it didn't work for some reason.

EDIT2: I tried the below , but both scalebox and scale aren't working

\documentclass[]{article}
\usepackage{algorithmic}
\usepackage{graphicx}

\usepackage{tikz}
\usetikzlibrary{shapes.geometric,
                arrows,
                positioning,
                arrows.meta,
                backgrounds,
                fit,
                matrix}

% image
\usepackage{svg}
\usepackage{subfigure}
\usepackage{xcolor}
\usepackage{booktabs} 
\usepackage{multirow}
\usepackage{siunitx}


% ----------------------------------------------------------------------------

\begin{document}


 \begin{figure*}[!t]
\centering
% \scalebox{0.5}{

\begin{tikzpicture}[xscale=0.5, yscale=0.5,transform shape,
    base/.style = {rectangle, draw, inner sep=2mm, align=center}, 
  steps/.style = {base, rounded corners, fill=gray!50, 
                  minimum height=1cm, text width=24mm},    % changed
 process/.style = {base,
                  minimum height=3cm, text width=34mm,     % changed 
                  fill=white},
 decision/.style  = {diamond, minimum height=1cm ,
                    draw=black, fill=white,text width=24mm,
                    inner sep=2mm, align = center},
 img/.style={inner sep=0pt,execute at begin node={%
    \includegraphics[width=4cm,height=4cm]{#1}}},%added
  >=Stealth 
                  ]
\matrix[matrix of nodes,column sep=1em,row sep=1em,nodes in empty cells,
nodes={anchor=center},
row 1/.style={nodes=steps,execute at begin node={Step \the\pgfmatrixcurrentcolumn}},
row 6/.style={nodes={text width=9em,align=center}}]
(mat) {
 & &  \\
 |[process]| text1 & 
 |[process]| text2 &
 |[process]| text3\\ 
 |[img=im]| & |[img=im]| & |[img=im]|  \\[1em]
 |[img=im]| & |[process]| & |[img=im]|  \\[1em]
 |[img=im]| & |[img=im]| & |[img=im]|  \\[-1em]
  &  &  \\
};
\scoped[on background layer]
{\foreach \X [count=\Y] in {black!2,black!5,black!15} {
 \node[fit=(mat-1-\Y) (mat-2-\Y) (mat-3-\Y) (mat-4-\Y) (mat-5-\Y) (mat-6-\Y), fill=\X]{};
}
}
\path[-Stealth]
(mat-2-1) edge (mat-2-2) 
(mat-2-2) edge (mat-2-3)
(mat-3-1) edge (mat-4-1)
(mat-4-1) edge (mat-5-1)
(mat-5-1) edge (mat-5-2)
(mat-5-2) edge (mat-4-2)
(mat-4-2) edge (mat-3-2)
(mat-3-2) edge (mat-3-3)
(mat-3-3) edge (mat-4-3)
(mat-4-3) edge (mat-5-3);
\end{tikzpicture}
% }
\end{figure*}
\end{document}

Answer 1

If you want to control the size of such a figure when including it, you can use standalone and tikzscale to include your example code (here saved under figure.tex) as a figure using the regular \includegraphics. See below for an example:

\documentclass{article}

\usepackage{tikz}
\usepackage{standalone} % Necessary to skip headers of {standalone} documents
\usepackage{tikzscale} % To use \includegraphics with TikZ code
\usetikzlibrary{backgrounds,fit,positioning}

\begin{document}

\includegraphics[width=1\linewidth]{figure.tex}

\includegraphics[width=0.8\linewidth]{figure.tex}

\includegraphics[width=0.4\linewidth]{figure.tex}

\end{document}

And the output: