The only thing that I want is a numbering out of colored box and the position of box be in center.
\documentclass{article}
\usepackage{amsmath,amsthm,amssymb,amsfonts}
\usepackage{tcolorbox}
\usepackage{tikz}
\tikzstyle{mybox} = [draw=green!70, fill=green!10, very thick, rectangle, rounded corners, inner sep=10pt, inner ysep=20pt]
\tikzstyle{fancytitle} =[fill=blue!70, text=white]
\begin{document}
\begin{tikzpicture}
\node[mybox](box){%
\begin{minipage}{0.9\textwidth}
\begin{equation}
L y=b \quad \quad Ux=y
\end{equation}
\end{minipage}
};
\end{tikzpicture}%
\end{document}
xepersianin your document,however ;-) – Jun 20 '16 at 09:42