# Remove white spacing before chapter styles modified with tcolorbox? (tufte-book)

In tufte-book, I have defined two chapter styles, one without numbering (used in front matter) and one with (used in main matter).

Now, there is unwanted white spacing before each style, as shown in the figure (showframe enabled). How to move the chapter to the immediate top of the document? That is, how to remove the unwanted vertical space?

Curiously, the spacing is different for each style. I am wondering what causes this?

Here is the MWE,

\RequirePackage{luatex85}
\documentclass[justified,notoc]{tufte-book}
\usepackage{tcolorbox}

\setcounter{secnumdepth}{0}

\title{Ngữ âm}
\author{Hiếu Nguyễn}
\publisher{Tự xuất bản}
\usepackage{showframe}
% For nicely typeset tabular material
\usepackage{booktabs}

\newcommand{\chapBox}[1]{\begin{tcolorbox}
[
colback=black!100,% background
colframe=black,% frame colour
coltext=white, % text color
width=\linewidth,%
height=0.5cm,
halign=left,
valign=center,
%fontupper=\large\bfseries,
enlarge top by=0mm,
enlarge bottom by=0mm,
arc=0mm, outer arc=0mm,
]
\Large\bfseries\allcaps{#1}
\end{tcolorbox}}

%%
\titleformat{\chapter}
[display]
{\chapBox{\chaptertitlename~\thechapter}}
{}
{0ex}
{\vspace{-0.7cm}\fontsize{28}{32}\raggedright\normalfont\color{orange}}

\titleformat{name=\chapter,numberless}
[display]
{}
{}
{0ex}
{\chapBox}

\titlespacing*{\chapter}{0pt}{0pt}{25pt}

\begin{document}
\frontmatter
\chapter{A frontmatter chapter}
\mainmatter
\chapter{A mainmatter chapter}
\end{document}


A figure showing what I am talking about.

\titlespacing*{name=\chapter,numberless}{0pt}{-35pt}{40pt}

to compensate the default used by the class; equivalent to \titlespacing*{\chapter}{0pt}{50pt}{40pt} (50pt above and 40pt bellow) plus titlesec own vertical added space.