\usepackage{pgfplots}
\usepackage[svgnames]{xcolor}
\usepgfplotslibrary{colorbrewer}

\pgfplotsset{
    compat=1.18,
    % forget plot = no legend
    edge/.style = {thick, gray!50!black,forget plot},
    data/.style = {mark=*, blue, only marks},
    backdata/.style = {mark=*, blue!30!white, only marks, onlyback, forget plot},
    iter1/.style = {mark=x, Crimson},
    iter2/.style = {mark=star, BlueViolet},
    iter3/.style = {mark=asterisk, DarkOliveGreen},
    backiter1/.style = {mark=x, Crimson!70!white, onlyback, forget plot},
    backiter2/.style = {mark=star, BlueViolet!70!white, onlyback, forget plot},
    backiter3/.style = {mark=asterisk, DarkOliveGreen!70!white, onlyback, forget plot},
    origin/.style = {mark=o, green, only marks, thick},
    surfstyle/.style = {very nearly opaque, forget plot},
    legend style = {
        inner sep = 0pt,
        outer xsep = 5pt,
        outer ysep = 0pt,
        legend cell align = left,
        align = left,
        draw = none,
        fill = none,
        font = \small
    },
    illustr3d/.style = {
        axis equal,
        width=5cm,
        height=5cm,
        scale only axis,
        enlargelimits=false,
        colormap access=map,
        colormap/Blues,
        colorbar,
        point meta rel=axis wide,
        shader = interp,
        xlabel = {$x$},
        ylabel = {$y$},
        zlabel = {$z$},
        ticks = none,
        axis line style = {draw=none},
        %axis x line = none,
        %axis y line = none,
        %axis z line = none,
        legend columns = 3,
        legend style = {
            at = {(0.5, 1.1)},
            anchor = north,
            column sep = 1ex,
        },
        mark size=1.5pt,
    }
}