Demonnic gave me this snippet a while back that draws a nice little box around your command line in the newer versions of mudlet and also in darkmood.
Put this in a script, name it anything. Put this in the working area
setCmdLineStyleSheet("main", [[
QPlainTextEdit{ /* QPlainTextEdit is used to prevent the styleSheet bleeding to the right click menu*/
border: 1px solid steelblue; /* Command line border style */
}}
]])
Change steelblue to whatever colour you like. Yay, little neat box.