Colouring table row: What is causing the colour to overflow table side margins? How to fix it?

Question

Here is the table in question:

• [Came during my attempting to answer this question (not relevant for this question). Improved by using leandriis's answer and Bernard's answer].

As we see, the colour overflows the table side margins.

1. What is causing this?
2. How to fix it? Minimally invasive procedure is preferred.

---

I have currently not reduced the MWE further to increase possibility that the solution works for the case at hand (lipsum part is removed).

\documentclass[12pt]{article}
\usepackage[labelsep=period, tableposition=top, labelfont=bf, singlelinecheck=false]{caption}
\usepackage[table]{xcolor} %for cell colour
\usepackage{booktabs}
\usepackage{makecell}
\usepackage{siunitx} %for the case when the table had lots of numbers to align (not used here)
\usepackage{threeparttable}
\makeatletter\usepackage{microtype}\g@addto@macro@verbatim{\microtypesetup{activate=false}}\makeatother%
\renewcommand\cellalign{cr} %align inside \makecell
\newcolumntype{N}{>{\global\let\currentrowstyle\relax}}
\newcolumntype{O}{>{\currentrowstyle}}
\newcommand{\rowstyle}[1]{\gdef\currentrowstyle{#1}%
  #1\ignorespaces
} %to make entire row boldface/color with one command instead of one at a time
\begin{document}
\begin{table}[!htbp]
\setlength{\extrarowheight}{1.5ex}
\centering
\begin{threeparttable}
    \caption{Title for your table goes here \vspace{-0.7em}}
    \begin{tabular}{@{} Nc|Oc|Oc|Oc|Oc @{}}
        \Xhline{0.1em}
        \rowstyle{\bfseries\cellcolor{cyan!70}} %here is where the colouring takes place
        {Parabola} & {Curve} & {Focus} & {Directrix} & {Vertex}\[1ex]
        \Xhline{0.07em}
        $x^2 = 4py$ & \makecell{up if $p > 0$ \ down if $p < 0$} & $F(0, p)$ & $y = -p$ & $V(0, 0)$\
        \Xcline{1-5}{0.03em}%horisontal line
        $y^2 = 4px$ & \makecell{right if $p > 0$\ left if $p < 0$} & $F(p, 0)$ & $x = -p$ & $V(0, 0)$\
        \Xhline{0.08em}
        \end{tabular}
    \label{table: label for table}
\end{threeparttable}
\end{table}
\end{document}

Answer 1

With {NiceTabular} of nicematrix and its built-in tools to color rows, cells and columns, you have directly the expected result.

However, in order to be able to use {NiceTabular} within {threeparttable}, one has to use first the dedicated hook of threeparttable:

\makeatletter
\AddToHook{env/threeparttable/begin}
{\TPT@hookin{NiceTabular}\TPT@hookin{NiceTabular*}}
\makeatother

In versions of LaTeX previous to 2020/10/01, the system of hooks was not available and you had to do that job with etoolbox instead:

\usepackage{etoolbox}
\makeatletter
\AtBeginEnvironment{threeparttable}{\TPT@hookin{NiceTabular}}
\makeatother

For the full MWE:

\documentclass[12pt]{article}
\usepackage[labelsep=period, tableposition=top, labelfont=bf, singlelinecheck=false]{caption}
\usepackage[table]{xcolor} %for cell colour
\usepackage{booktabs}
\usepackage{makecell}
\usepackage{siunitx} %for the case when the table had lots of numbers to align (not used here)
\usepackage{threeparttable}
\usepackage{nicematrix}
\makeatletter\usepackage{microtype}\g@addto@macro@verbatim{\microtypesetup{activate=false}}\makeatother%
\renewcommand\cellalign{cr} %align inside \makecell
\newcolumntype{N}{>{\global\let\currentrowstyle\relax}}
\newcolumntype{O}{>{\currentrowstyle}}
\newcommand{\rowstyle}[1]{\gdef\currentrowstyle{#1}%
  #1\ignorespaces
} %to make entire row boldface/color with one command instead of one at a time
\makeatletter
\AddToHook{env/threeparttable/begin}
{\TPT@hookin{NiceTabular}\TPT@hookin{NiceTabular*}}
\makeatother
\begin{document}
\begin{table}[!htbp]
\setlength{\extrarowheight}{1.5ex}
\centering
\begin{threeparttable}
    \caption{Title for your table goes here \vspace{-0.7em}}
    \begin{NiceTabular}{@{} Nc|Oc|Oc|Oc|Oc @{}}
    \CodeBefore
      \rowcolor{cyan!70}{1}
    \Body
        \Xhline{0.1em}
        \rowstyle{\bfseries} %here is where the colouring takes place
        {Parabola} & {Curve} & {Focus} & {Directrix} & {Vertex}\[1ex]
        \Xhline{0.07em}
        $x^2 = 4py$ & \makecell{up if $p > 0$ \ down if $p < 0$} & $F(0, p)$ & $y = -p$ & $V(0, 0)$\
        \Xcline{1-5}{0.03em}%horisontal line
        $y^2 = 4px$ & \makecell{right if $p > 0$\ left if $p < 0$} & $F(p, 0)$ & $x = -p$ & $V(0, 0)$\
        \Xhline{0.08em}
    \end{NiceTabular}
    \label{table: label for table}
\end{threeparttable}
\end{table}
\end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).

Answer 2

I suggest using \columncolor because you have optional arguments for the colour overhangs on each side of the cells, combined with a \rowcolors{2}{white}{white} to neutralise colouring after the column heads:

\documentclass[12pt]{article}
\usepackage[labelsep=period, tableposition=top, labelfont=bf]{caption}
\usepackage[table]{xcolor} %for cell colour
\usepackage{booktabs}
\usepackage{makecell}
\usepackage{tabu} %for \cellcolor to work inside \rowstyle
\usepackage{siunitx} %for the case when the table had lots of numbers to align (not used here)
\makeatletter\usepackage{microtype}\g@addto@macro@verbatim{\microtypesetup{activate=false}}\makeatother%
\usepackage{floatrow, caption}
\renewcommand\cellalign{cr} %align inside \makecell
\newcolumntype{N}{>{\global\let\currentrowstyle\relax}}
\newcolumntype{O}{>{\currentrowstyle}}
\newcommand{\rowstyle}[1]{\gdef\currentrowstyle{#1}%
  #1\ignorespaces
} %to make entire row boldface/color with one command instead of one at a time
\usepackage{lipsum}
\begin{document}
\lipsum[11]
\begin{table}[!htbp]
\captionsetup{singlelinecheck=false}\setlength{\extrarowheight}{2ex}
    \centering
    \ttabbox{\rowcolors{2}{white}{white}\begin{tabular}{@{}>{\columncolor{cyan!70}[0pt][\tabcolsep]}Nc|*{3}{>{\columncolor{cyan!70}}Oc|}>{\columncolor{cyan!70}[\tabcolsep][0pt]}Oc @{}}
        \Xhline{0.08em}
        %\rowstyle{\bfseries\cellcolor{cyan!70}}
        {Parabola} & {Curve} & {Focus} & {Directrix} & {Vertex}\[1.5ex]
        \Xhline{0.05em}
       $x^2 = 4py$ & \makecell{up if $p > 0$ \ down if $p < 0$} & $F(0, p)$ & $y = -p$ & $V(0, 0)$\[1.5ex]
        \Xhline{0.03em}%horizontal line
        $y^2 = 4px$ & \makecell{right if $p > 0$\ left if $p < 0$} & $F(p, 0)$ & $x = -p$ & $V(0, 0)$\[1.5ex]
        \Xhline{0.08em}
        \end{tabular}}{%
    \caption{A very very long title for your table goes here and nowhere else. }
    \label{table: label for table}}
\end{table}
\end{document}