What is pixel perfect design? is it not responsive? i saw many tutorials on youtube ( figma to html css) and all of them are using the same css which is defined in figma for each components. like 283px and 90px width for a box. My question is how can i make this responsive if it is fixed in pixels? if i make 3 layouts of design ( mobile ,tab, desktop) then it works properly on these specific resolutions but don't work properly between those 3 (mobile,tab,desktop) resolution. If i use rem, it doesn't work responsive. I want to learn how to code Figma/xd/psd to HTML CSS.
Responsive Design is a topic in of itself and you seem to have little prior knowledge about it. There are many web frameworks and practices that help you create responsive designs. Without an example of what exactly you are trying to achieve it is hard to help you. Let me try anyway:
You are correct about absolute units not changing upon device-size. The best ways to have responsive code straight out of Figma is to make a lot of use of its constraints. You can set sizes to scale with the parent, keep left and right margins, use auto layouts (translates to flexbox css) and so on...
In general css provides you some relative units like %, em, rem, vw and vh: https://fullscale.io/blog/best-css-unit-for-responsive-web-design/
rem is relative to the root- element's font-size.
em is relative to the parent element's font-size.
% is simply the percentage of the parent element's width.
vw and vh are the percentage of the viewport's width and height.
I'd also suggest you look up @media breakpoints which are a way to apply css styles to different device sizes: https://www.w3schools.com/howto/howto_css_media_query_breakpoints.asp
/* Extra small devices (phones, 600px and down) */
@media only screen and (max-width: 600px) {...}
/* Small devices (portrait tablets and large phones, 600px and up) */
@media only screen and (min-width: 600px) {...}
/* Medium devices (landscape tablets, 768px and up) */
@media only screen and (min-width: 768px) {...}
/* Large devices (laptops/desktops, 992px and up) */
@media only screen and (min-width: 992px) {...}
/* Extra large devices (large laptops and desktops, 1200px and up) */
@media only screen and (min-width: 1200px) {...}