Vertical color background of section title

Question

Good night. It's my problem about gradient colored section title, with vertical length. It's codes are,

\documentclass{scrbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
\usepackage[svgnames]{xcolor}
\usepackage{lipsum}
\usepackage[explicit]{titlesec}
\usepackage{tikz}

\titleformat{\section}[block]%        
{\normalsize\bfseries\itshape\tikz[overlay] \shade[left color=red!20!yellow,right color=black!40!white] (0,-1ex) rectangle  (\linewidth,1em);}%
{\thesection}%                   
{1em}%
{\color{Maroon}#1}

\begin{document}
\section{A textwidth section - OK.}
\lipsum[1]
\section{A very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very long section - NOT OK.}
\lipsum[1]
\section{A section header full of \lipsum[1]}
\end{document}

But, It is not coloring all of second section. Related HTML pages not exactly for me. Therefore what is the simple code block that should be added this code?

Related:

Format section titles as white text on black background

Section title gradient

How to draw a gradient box around sections

Answer 1

Caramdir's answer can be adopted easily to your case.

\documentclass[svgnames]{scrbook}
\usepackage{tikz,lipsum}
\usepackage{lipsum}
\usepackage{titlesec}
\usetikzlibrary{calc}

\pgfdeclarelayer{background}
\pgfsetlayers{background,main}

\newcommand\boxedsection[1]{{%
    \usekomafont{sectioning}\usekomafont{section}%
    \begin{tikzpicture}[inner sep=0pt, inner ysep=0.3ex]
        \node[anchor=base west] at (0,0) (counter) {\thesection};
        \path let \p1 = (counter.base east) in node[anchor=base west, text width={\textwidth-\x1-0.33em},text=Maroon] (content) at ($(counter.base east)+(0.33em,0)$) {#1};
        \begin{pgfonlayer}{background}
            \shade[left color=red!20!yellow,right color=black!40!white] let \p1=(counter.north), \p2=(content.north) in
            (0,{max(\y1,\y2)}) rectangle (content.south east);
        \end{pgfonlayer}
    \end{tikzpicture}%
}}

\titleformat{\section}%
    {}%
    {}%
    {0pt}%
    {\boxedsection}%

\begin{document}
\section{A textwidth section - OK.}
\lipsum[1]
\section{A very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very long section - NOT OK.}
\lipsum[1]
\end{document}

And if you want to modify your code so that it works use the following:

\documentclass[a4paper,twoside,openright,11pt]{scrbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
\usepackage[svgnames]{xcolor}
\usepackage{lipsum}
\usepackage[explicit]{titlesec}
\usepackage{tikz,showframe}

\titleformat{\section}[block]%
{\normalsize\bfseries\itshape}%
{}%
{0em}%
{\tikz\node[left color=red!20!yellow,right color=black!40!white,text=Maroon,inner xsep=0pt,outer sep=0pt,text width=\linewidth,] {\thesection \space #1};}

\begin{document}
\chapter{Chapter One}
\section{Section One}
\section{Section Two}
\section{Mass of this entire universe and me are not equal as I am a part of the universe}

\end{document}