I borrowed this code from Clean Thesis template with a small modification in color selection.
\documentclass[b5paper,11pt]{scrbook}
\usepackage{lipsum}
\usepackage{mathpazo}
\usepackage{xcolor}
\renewcommand*\chapterheadstartvskip{\vspace*{-8.75em}}
\renewcommand*\chapterheadendvskip{\vspace*{2.5\baselineskip}}
\renewcommand*{\chapterformat}{%
\ctchapternumber{\thechapter}%
}
\renewcommand{\chapterlinesformat}[3]{%
\ctchaptertitle{#3}%
#2%
}
\newcommand{\ctchapternumber}[1]{%
\usekomafont{chapter}%
\begin{minipage}[t]{0.3\textwidth}%
\raggedleft{%
{\color{red!50!black}\rule[-5pt]{2pt}{5cm}}%
\quad%
{\color{red!50!black}\fontsize{60}{60}\selectfont#1}%
}%
\end{minipage}%
}
\newcommand{\ctchaptertitle}[1]{%
\usekomafont{chapter}%
\begin{minipage}[t]{0.7\textwidth}%
\vspace*{5.85em}%
\raggedright%
#1%
\end{minipage}%
}
\begin{document}
\chapter{Introduction}
\lipsum[1]
\end{document}
This is the result I get.
As you can see, I already used font size 60 for chapter number but It doesn't get any bigger. It seems \fontsize{60}{60}
has no effect on the chapter number font size. How do fix this?