How can and I read and write css files

[snippsat]

CSS is just a text format,so can read and write in stander way.
If you are not taking about how a web-framework read a CSS file?

style.css

Output:
body {
  background: #67B26F;
}

html {
  height: 100%
}

#wrapper {
  width: auto;
}

with open('style.css') as f:
    css_file = f.read()

new = css_file.replace('html', 'rubberduck')

with open('new.css', 'w') as f_out:
    f_out.write(new)

new.css

Output:
body {
  background: #67B26F;
}

rubberduck {
  height: 100%
}

#wrapper {
  width: auto;
}