Live editor for CSS and LESS - Magic CSS
DarDreams last edited by
Auto apply does not work
webextensions last edited by
The process for extension approval for Opera (and Firefox) have been too much time-taking and/or restrictive. So, the version there in Opera is pretty outdated. Because of that, I didn't spend much time in updating there.
Since in Opera one can also install Chrome extensions, I would recommend directly installing it from https://chrome.google.com/webstore/detail/live-editor-for-css-less/ifhikkcafabcgolfjegfcgloomalapol
I hope that helps.