\@startsection defaults ¶These are LaTeX’s defaults for the first three sectioning units that
are defined with \@startsection, for the article,
book, and report classes.
section: level is 1, indent is 0pt,
beforeskip is -3.5ex plus -1ex minus -0.2ex,
afterskip is 2.3ex plus 0.2ex, and style is
\normalfont\Large\bfseries.
subsection: level is 2, indent is 0pt,
beforeskip is -3.25ex plus -1ex minus -0.2ex,
afterskip is 1.5ex plus 0.2ex, and style is
\normalfont\large\bfseries.
For subsubsection: level is 3, indent is 0pt,
beforeskip is -3.25ex plus -1ex minus -0.2ex,
afterskip is 1.5ex plus 0.2ex, and style is
\normalfont\normalsize\bfseries.