why does my css look very different in literally every browser/even window? (neocities)

Question

i use brackets but when i copy-paste my code onto neocities it looks different and i uhmm dont know how to fix it...also sorry if my english is wonky ;-;

this is how it looks like on private google chrome window and this is how i want it to look

this is how it looks like on a regular google chrome window

the background is gone + the paddings etc are wayy too off + the background of the chat cell is gone for good + corner rounding for cells is gone as well

and this is how it looks like on safari!

the width of the table is off

heres the link to my site https://pamirsareopagos.neocities.org/main.html