Tikz diagram help

\documentclass{standalone}
\usepackage{tikz}
\usepackage{tikz-3dplot}

\begin{document}

% Set azimuth and elevation for the 3D view
\def\az{110}
\def\elev{70}
\tdplotsetmaincoords{\elev}{\az}

\begin{tikzpicture}[tdplot_main_coords, line join=round]

  % Cylinder parameters
  \def\r{0.5}
  \def\h{2}

  % Base plate (cuboid)
  \draw (-4,-1,-0.5) -- (4,-1,-0.5);
  \draw (4,-1,-0.5) -- (4,1,-0.5);
  \draw (4,1,-0.5) -- (-4,1,-0.5);
  \draw[fill=white] (-4,-1,0) -- (4,-1,0) -- (4,1,0) -- (-4,1,0) -- cycle;
  \draw (4,1,0) -- (4,1,-0.5);
  \draw (4,-1,0) -- (4,-1,-0.5);
  \draw (-4,1,0) -- (-4,1,-0.5);

  % Coordinate axes
  \draw[->] (-6,0,0) -- (6,0,0) node[anchor=north east] {$z$};
  \draw[->] (0,-2,0) -- (0,2,0) node[anchor=south west] {$x$};
  \draw[->] (0,0,\h) -- (0,0,3) node[anchor=south] {$y$};

  % Vertical cylinder
  \draw[fill=white]
    ({cos(\az+180)*\r},{sin(\az+180)*\r},\h) -- ({cos(\az+180)*\r},{sin(\az+180)*\r},0) --
    ({cos(\az+180)*\r},{sin(\az+180)*\r},0) arc[start angle=\az+180, end angle=470, x radius=\r, y radius=\r] --
    ({cos(\az)*\r},{sin(\az)*\r},0) -- ({cos(\az)*\r},{sin(\az)*\r},\h);

  % Top ellipse of the cylinder
  \draw (0,\r,\h) arc[start angle=90, end angle=450, x radius=\r, y radius=\r];

  % Hidden coordinate lines (dashed)
  \draw[densely dashed] (-4,0,0) -- (\r,0,0);
  \draw[densely dashed] (0,-\r,0) -- (0,\r,0);
  \draw[densely dashed] (0,0,-0.5) -- (0,0,\h);

  % Origin marker
  \node[fill, circle, inner sep=1pt, label=above left:$O$] (O) at (0,0,0) {};

  % Top center of the cylinder
  \fill (0,0,\h) circle (0.7pt);

\end{tikzpicture}

\end{document}