add absolute position box to latex document

abs-pos-box.tex

% before begin{document}
\usepackage[absolute]{textpos}

% after begin{document}
% first arg is width of box
% second arg is (vertical,horizontal) position
\begin{textblock}{13.5}(1,0.25)\fbox{
\begin{minipage}{\dimexpr\textwidth-2\fboxsep-2\fboxrule\relax}
\scriptsize
Text here
\end{minipage}}\end{textblock}

example usage, top "please use the eurosys reference" box at the top of the first page: https://arxiv.org/abs/2011.01258