How to draw tcolorbox without a frame?

Question

I'm trying this:

\documentclass{article}
\usepackage{tcolorbox}
\begin{document}
\begin{tcolorbox}[boxrule=0pt,frame hidden]
Hello, world!
\end{tcolorbox}
\end{document}

But still, can see a thin frame around it.

Answer 1

What Ulrike suggested (add enhanced option and skins library) is the best solution.

Alternatively, you could try with frame empty, without any library.

\documentclass{article}
\usepackage{tcolorbox}
\begin{document}
\begin{tcolorbox}[boxrule=0pt, frame empty]
Hello, world!
\end{tcolorbox}
\end{document}

Or with opacityframe=0, skins library is needed here:

\documentclass{article}
\usepackage[skins]{tcolorbox}
\begin{document}
\begin{tcolorbox}[boxrule=0pt, opacityframe=0]
Hello, world!
\end{tcolorbox}
\end{document}

In both cases, the result is:

Answer 2

Full customized box:

\documentclass{book}
\usepackage[english]{babel} %
\usepackage{graphicx} %
\usepackage{xcolor}
\usepackage{pgfkeys}
\usepackage{tcolorbox}
%
\setlength{\unitlength}{1mm}
%
\definecolor{DarkRed}{rgb}{0.45,0.00,0.00}
\definecolor{LightGrey}{rgb}{0.96,0.96,0.96}
% define the options
\pgfkeys{%
  /mybox/.is family, /mybox/.cd,
  background color/.code={\colorlet{bgcolor}{#1}},
  frame color/.code={\colorlet{framecolor}{#1}},
  frame sep/.code={\setlength{\fboxsep}{#1}},
  frame width/.code={\setlength{\fboxrule}{#1}},
  % initialize colors
  background color=white,
  frame color=black
}
% universal box
\newcommand{\mybox}[2][]{%
  \begingroup
  \pgfkeys{mybox,#1}%
  \fcolorbox{framecolor}{bgcolor}{#2}%
  \endgroup
}
\newcommand{\redbox}[1]{%
 \mybox[frame width=0.75pt,
        frame sep=4.8pt,
        frame color=white,
        background color=red!40]{#1}}
\begin{document}
\noindent \redbox{Some ordinary text $+\hspace{1.2pt}x^{\hspace{0.6pt}2}$}
\end{document}