fltk4lua is easy for simple stuff like that, yea.
#! /usr/bin/env lua
-- sudo apt install libfltk1.3-dev
-- luarocks install fltk4lua
local fl = require( 'fltk4lua' )
fl .scheme( 'gtk+' )
local Width, Height = 300, 200
local Title = 'Lua Output'
local window = fl .Window( Width, Height, Title )
local icon = fl .Chart{ Width *0.1, Height *0.1, 100, 100, type = FL_BAR_CHART }
local text = fl .Box{ Width *0.5, Height *0.3, 100, 30, 'Hello World!' }
local button = fl .Button{ Width *0.5, Height *0.75, 100, 30, 'Okay' }
icon :add( 6, 6, 0x05 ) -- www.fltk.org/doc-1.3/drawing.html#drawing_colors
icon :add( 5, 5, 0x04 )
icon :add( 4, 4, 0x02 )
icon :add( 3, 3, 0x01 )
window :end_group()
window :show( arg )
fl .run()