Same result, but done at the package level, using tikz pagenodes, and setting the border command as the page header with fancyhdr
, so you can add in other header material if you need to.

Perhaps easier to maintain and modify, semantically speaking, depending on your coding style. Only two variables, colour and line width (with the "frame's" given x- and y-shift of 0).
I find no additional overhead loading tikz
, so this solution may depend on your system constraints (if any).
MWE
\documentclass{article}
\usepackage{tikz}
\usepackage{tikzpagenodes}
\usepackage{fancyhdr}
\usepackage{lipsum}
\newcommand{\gborder}{\tikz[remember picture,overlay]
\draw [black!10!blue!20,line width=18mm]
(current page.south west)
rectangle
(current page.north east)
;}
\pagestyle{fancy}
\fancyhead{}
\fancyfoot{}
\fancyhead[C]{\gborder}
\renewcommand{\headrule}{}
\begin{document}
\section{A}
\lipsum[1-10]
\section{B}
\lipsum[1-10]
\end{document}