i build with css pure, was maybe easy but i dont know all margins :(

To center a content on a page, add min-height:100vh; display: flex; align-items-center: justify-content: center; to the body.

There is no need for a height value and a margin value .caja , give .caja a padding value, this will help. paddings are for inside and margins are for outside : .caja{padding:20px;}

Give .qr width:100% or max-width:100% and a border-radius, there is no need for a margin value and display: flex; and it properties.

There is no need to give . parafo and .info a height value , width value and display: flex; give . info a margin bottom value and remove margin: auto, for the color of .info give it opacity of 0.5 or 0.7 and remove the color : .info{margin-bottom:20px; opacity:0.7}

Use rem or em as unit for the padding , margin, width and preferably rem for the font-size for more on this watch this https://youtu.be/N5wpD9Ov_To

Hope am helpful HAPPY CODING