I have a very simple template of a table
I would like to add a slashbox at the top left corner (entry|item), similar to this post LaTeX table cell with a diagonal line and 2 sub cells
However, I have tried to add their code on top of the code below, yet I was not able to make it work.
Can someone provide a simple solution that creates a slashbox / diagonal line for this table?
\documentclass{article}
\usepackage{xcolor}
\usepackage{bbding}
\usepackage{amsthm, thmtools}
\usepackage{mathtools}
\usepackage{steinmetz}
\usepackage{amsmath,amssymb,amsfonts}
\usepackage{graphics}
\usepackage{cancel}
\usepackage{subcaption}
\usepackage{sidecap}
\usepackage{setspace}
\usepackage{verbatim}
\everymath{\displaystyle}
\setlength\parindent{0pt}
\setlength{\footskip}{40pt}
\begin{document}
\begin{center}
\centering\begin{tabular}{ |p{3cm}||p{2cm}|p{2cm}|p{2cm}|p{2cm}|}
\hline
& entry 1 & entry 2 & entry 3 & entry 4 \\
\hline
item 1 & $\%$ & $\%$ & $\%$ & $\%$\\
\hline
item 2 & $\%$ & $\%$ & $\%$ & $\%$\\
\hline
item 3 & $\%$ & $\%$ & $\%$ & $\%$\\
\hline
item 4 & $\%$ & $\%$ & $\%$ & $\%$\\
\hline
\end{tabular}\\
\end{center}
\end{document}



\everymath{\displaystyle}?(it makes inline math essentially unusable as inline math, although it can be useful for some special situations where you need to use inline math for technical reasons but want it to look like display – David Carlisle Nov 28 '17 at 22:55