documentclass{book}
usepackage{fourier}% change to lmodern if fourier is no available
usepackage{tikz}
usepackage[explicit]{titlesec}

definecolor{mybluei}{RGB}{0,173,239}
definecolor{myblueii}{RGB}{63,200,244}
definecolor{myblueiii}{RGB}{199,234,253}

renewcommandthepart{arabic{part}}

newcommandpartnumfont{% font specification for the number
  fontsize{380}{130}color{myblueii}selectfont%
}

newcommandpartnamefont{% font specification for the name "PART"
  normalfontcolor{white}scshapesmallbfseries
}

titleformat{part}
  {normalfonthugefilleft}
  {}
  {20pt}
  {begin{tikzpicture}[remember picture,overlay]
  fill[myblueiii]
    (current page.north west) rectangle ([yshift=-13cm]current page.north east);
  node[
      fill=mybluei,
      text width=2paperwidth,
      rounded corners=6cm,
      text depth=18cm,
      anchor=center,
      inner sep=0pt] at (current page.north east) (parttop)
    {thepart};%
  node[
      anchor=south east,
      inner sep=0pt,
      outer sep=0pt] (partnum) at ([xshift=-20pt]parttop.south)
    {partnumfontthepart};
  node[
      anchor=south,
      inner sep=0pt] (partname) at ([yshift=2pt]partnum.south)
  {partnamefont PART};
  node[
      anchor=north east,
      align=right,
      inner xsep=0pt] at ([yshift=-0.5cm]partname.east|-partnum.south)
  {parbox{.7textwidth}{raggedleft#1}};
  end{tikzpicture}%
  }

begin{document}

part{Theory and Application of Continuous-Time Signals and Systems}

end{document}