documentclass{article}
usepackage{tikz}
usetikzlibrary{calc}
newcommand{mybox}[2]{
begin{tikzpicture}
node[minimum width = linewidth, text = white] (title) {bfseriesLarge #1};
node[minimum width = linewidth, anchor = north] at (title.south) (main frame) {parbox{.95linewidth}{#2}};

draw[line width= 0.25mm] (title.north west) -- (main frame.south west) -- (main frame.south east) -- (title.north east);

filldraw[fill = blue, line width= 0.25mm]
let p1 = (title.south west),
p2 = (title.north west),
p3 = (title.south east),
p4 = (title.north east) in
(x2, y2) arc (90:0:0.5*y2-0.5*y1) arc (180:270:0.5*y2-0.5*y1) -- (x3 - y2 + y1, y1) arc (270:360:0.5*y2-0.5*y1) arc (180:90:0.5*y2-0.5*y1) -- cycle;
draw[text = white] node at (title){bfseriesLarge #1};
end{tikzpicture}
}

begin{document}
mybox{TITLE}{
Many paragraphs

can

go

in content.
}
end{document}