scrlttr2 same head back filled as my CV

Question

Lately I just found the scrlttr2 class for my letters, as it has the SN option that gets all I need, in less than 5-10 seconds. But if I would like to use it to make my CV cover letter, I need one particular option, to be able to draw a color background for my heading.

The thing is I played with the pirates engineer template (https://www.overleaf.com/latex/templates/pirate-engineer-template/sqfvydxkztqj), getting a decent CV, and I would like to find a way to keep the letter as profesional as it is, with my little personal touch.

So how can I draw the same kind of colored stripe with white colored text using the from * macros/variable already present?

I tried adding TikZ packages and drawing some tabular or parbox, but it just shift my letter on the second page, while the first gets a shifted (by firstheadvpos and firstheadhpos) colorfilled rectangle, seemingly at the place of the heading, maybe going over the right margin (as I used minimum width=\paperwidth in the TikZ setup).

MWE:

%\LoadLetterOption{SN} %% Lettere in stile svizzero
\usepackage{mwe}
\usepackage{geometry}

\usepackage[italian]{babel}
\usepackage{hyperref}

\usepackage{xcolor}
\definecolor{Green4}{HTML}{059108}

\usepackage{calc}

%% advanced drawing
\usepackage{tikz}
\usepackage{tikz-3dplot}
\usepackage{smartdiagram}
\usepackage{float}
\usepackage{array}
\usetikzlibrary{decorations.text}
\usetikzlibrary{fadings}
\usetikzlibrary{calc}
\usetikzlibrary{shapes.misc,positioning}
\usetikzlibrary{arrows}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{backgrounds} 
\usetikzlibrary{shadings}
\usetikzlibrary{calendar} 
\usetikzlibrary{er}
\usetikzlibrary{patterns}
\usetikzlibrary{shapes} 
\usetikzlibrary{shapes.geometric}
\usetikzlibrary{decorations}
\usetikzlibrary{topaths}

\renewcommand{\familydefault}{\sfdefault}

\date{\today}

\KOMAoptions{
    paper=a4,
    fromemail=true,
    foldmarks=true,
    fromphone=true,
    firsthead=true,
%   backaddress=false,
}

%% Opzioni personali
\setkomavar{fromname}{First LAST}
\setkomavar{fromaddress}{my Street\\ZIP myCity}
\setkomavar{fromemail}[]{\href{mailto:[email protected]}{[email protected]}}
\setkomavar{fromphone}[]{+41 (0)7x abc de fg}
\setkomavar{place}{myLivingRoom}
\setkomavar{signature}{f. LAST}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%
%%%%    Oggetto della missiva
%%%%
\setkomavar{subject}{Job something}
%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    \firsthead{
        \tikz{%
            \node[rectangle, fill=Green4, anchor=north, minimum width=\paperwidth, minimum height=3.5cm](header) at (current page.north){};%
            \node[draw=none, align=left](name) at (header) {%
                {\color{white}\usekomavar{fromname}\\ \usekomavar{fromaddress}}% 
                    };%
            \node[draw=none, align=right](contacts) at (header) {\color{red}\usekomavar{fromphone}\\ \usekomavar{fromemail}};% 
        }\vspace{-7mm}%
    }
    
\begin{document}
    % If you want headings on subsequent pages,
    % remove the ``%'' on the next line:
    % \pagestyle{headings}
    

    \begin{letter}{\textbf{COmpany Hiring}\\companyStreet\\ZipCode Town}
        
        \opening{Dear Madam, Dear Sir,}
        
        
        
        \closing{Best Regards,}
        
        %enclosure listing
        \vfill
        \encl{CV}
        
    \end{letter}
\end{document}

Output: Desired output:

Answer 1

You have to add options remember picture and overlay for the \tikz command (or the tikzpicture environment) and you have to use anchors for the nodes.

\documentclass{scrlttr2}
%\LoadLetterOption{SN} %% Lettere in stile svizzero

\usepackage[T1]{fontenc}% <- added
\usepackage{tikz}% loads package xcolor
\usepackage{hyperref}

\definecolor{Green4}{HTML}{059108}

\renewcommand{\familydefault}{\sfdefault}

\setkomavar{date}{\today}% <- changed!

\KOMAoptions{
    %paper=a4,% default
    fromemail=true,
    foldmarks=true,
    fromphone=true,
    firsthead=true,
%   backaddress=false,
}

%% Opzioni personali
\setkomavar{fromname}{First LAST}
\setkomavar{fromaddress}{my Street\\ZIP myCity}
\setkomavar{fromemail}[]{\href{mailto:[email protected]}{[email protected]}}
\setkomavar{fromphone}[]{+41 (0)7x abc de fg}
\setkomavar{place}{myLivingRoom}
\setkomavar{signature}{f. LAST}

\setkomavar{subject}{Job something}

\setkomavar{firsthead}{% <- changed!
  \tikz[remember picture,overlay,inner sep=1em,text=white]{
    \node[outer sep=0pt,fill=Green4, anchor=north, minimum width=\paperwidth, minimum height=3.5cm]
      (header) at (current page.north) {};%
    \node[anchor=north west,align=left](name) at (header.north west) 
      {\usekomavar{fromname}\\ \usekomavar{fromaddress}};%
    \node[anchor=north east,align=left](contacts) at (header.north east)
      {\usekomavar{fromphone}\\ \usekomavar{fromemail}};% 
  }%
}

\begin{document}
\begin{letter}{\textbf{COmpany Hiring}\\companyStreet\\ZipCode Town}
  \opening{Dear Madam, Dear Sir,}
  \closing{Best Regards,}
  \vfill
  \encl{CV}
\end{letter}
\end{document}

Note, that I have used \setkomavar{date}{...} and \setkomavar{firsthead}{...}.