\documentclass{standalone}
\standaloneconfig{margin=2mm}

\usepackage{pgfplots}
\pgfplotsset{compat=1.15}
\usepackage{mathrsfs}
\usetikzlibrary{arrows}
\pagestyle{empty}
\begin{document}
\definecolor{qqqqff}{rgb}{0.,0.,1.}
\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1.0cm,y=1.0cm]
\begin{axis}[
x=1.0cm,y=1.0cm,
axis lines=middle,
ymajorgrids=true,
xmajorgrids=true,
xmin=-4.3,
xmax=18.599999999999998,
ymin=-6.26,
ymax=6.3,
xtick={-4.0,-3.0,...,18.0},
ytick={-6.0,-5.0,...,6.0},]
\clip(-4.3,-6.26) rectangle (18.6,6.3);
\draw[line width=2.pt,dash pattern=on 2pt off 2pt,color=qqqqff,fill=qqqqff,fill opacity=0.25](-4.3,2.65)--(-4.3,-6.26)--(4.94,-6.26)--(4.94,-1.97)--(-4.3,2.65);
\end{axis}
\end{tikzpicture}
\end{document}

\documentclass{standalone}
\standaloneconfig{margin=2mm}

\usepackage{pgfplots}
\pgfplotsset{compat=1.15}
\usepackage{mathrsfs}
\usetikzlibrary{arrows}
\pagestyle{empty}
\begin{document}
\definecolor{qqqqff}{rgb}{0.,0.,1.}
\begin{tikzpicture}[line cap=round,line join=round,>gt;=triangle 45,x=1.0cm,y=1.0cm]
\begin{axis}[
x=1.0cm,y=1.0cm,
axis lines=middle,
ymajorgrids=true,
xmajorgrids=true,
xmin=-4.3,
xmax=18.599999999999998,
ymin=-6.26,
ymax=6.3,
xtick={-4.0,-3.0,...,18.0},
ytick={-6.0,-5.0,...,6.0},]
\clip(-4.3,-6.26) rectangle (18.6,6.3);
\draw[line width=2.pt,dash pattern=on 2pt off 2pt,color=qqqqff,fill=qqqqff,fill opacity=0.25](-4.3,2.65)--(-4.3,-6.26)--(4.94,-6.26)--(4.94,-1.97)--(-4.3,2.65);
\end{axis}
\end{tikzpicture}
\end{document}