How to make text readable on mobile devices?

Question

css

Created a product description on Ebay (html/css - adaptive layout). Despite the fact that the description is "responsive", when visiting the ad on a mobile device (through the application), everything looks not very convenient. Namely: when you click "read more" in the description, ebay opens the typed description in a new, so to speak, window.
How to make it so that when the screen resolution is less than I set, the design is replaced by text (which I prepared)
We need not an adaptive layout (since it already is), but a replacement. So that all the pictures in the description and links, everything changes to bare text, but not the one that was originally in the layout).
Example: on devices with "such and such" permission, there will be a designed product description, but if you go to the description from a mobile device, there will be only bare text different from the designed page.
I hope I made it clear.
Thank you!

Answer 1

meta:viewport in head ?

Answer 2

What you call replacement is responsive layout.
Create all the blocks in the description at once, both for desktops and mobiles.
Set the css for desktops to mobile blocks to display : none.
And vice versa. For example:
media only screen and (max-width: 760px) and (orientation: portrait) {
.desktop_block {display:none}
}