A pretty typography for an enumeration with the latin fonts into rounded square

Question

I have this MWE

\documentclass[12pt]{article}
\usepackage{mathtools}
\usepackage{enumitem}
\begin{document}
\begin{enumerate}[label=\alph*\addtocounter{enumi}{0}]
\item First item.
\item Second item. 
\item Third item. 
\end{enumerate}
\end{document} 

with this output,

I would like to replace the classic letters of the Latin alphabet starting with the letter a as the style taken from the following image

into the label environment [label=\alph*\addtocounter{enumi}{0}].

Thank you for your precious help.

Possible related:

1. A new and better aesthetic look for figures and captions with vertical braces
2. Center a rounded square into a green line

Answer 1

If you can do without the rounded corners, here is a simple solution:

\documentclass[12pt]{article}
\usepackage{mathtools}
\usepackage{enumitem}
\usepackage[svgnames]{xcolor}

\begin{document}

\begin{enumerate}[label=\colorbox{LightGoldenrod}{\color{white}\alph*}, font=\sffamily\bfseries, before={\fboxsep=5pt}]
\item First item.
\item Second item.
\item Third item.
\end{enumerate}

\end{document}

Answer 2

All I did was to combine Jasper's link (which has a friendly reminder that one should use \protect here) with the second of your links to get

\documentclass[12pt]{article}
\usepackage{enumitem}
\usepackage{tikz}
\newcommand{\SebastianoBox}[1]{\tikz[baseline={(B.base)}]{%
\node[fill=green!80!black,text=white,font=\bfseries\sffamily\large,rounded
corners=0.2em,minimum width=1.8em,minimum height=1.8em](B){#1};}}
\begin{document}
\begin{enumerate}[label=\protect\SebastianoBox{\alph*\addtocounter{enumi}{0}}]
\item First item.
\item Second item. 
\item Third item. 
\end{enumerate}
\end{document} 

And here is a smaller version.

\documentclass[12pt]{article}
\usepackage{enumitem}
\usepackage{tikz}
\newcommand{\SebastianoBox}[1]{\tikz[baseline={(B.base)}]{%
\node[fill=green!80!black,text=white,font=\bfseries\sffamily,rounded
corners=0.15em,inner xsep=0.2em,inner ysep=0.1em,align=center,text depth=0.2em,
text height=0.8em,text width=0.8em](B){#1};}}
\begin{document}
\begin{enumerate}[label=\protect\SebastianoBox{\alph*\addtocounter{enumi}{0}}]
\item First item.
\item Second item. 
\item Third item. 
\end{enumerate}
\end{document}