WPYogi is right. You shouldn’t edit Theme files directly, because if/when you update your theme, your changes will be overwritten.
If you create a child theme of the theme you’re currently using, you can overrule the styles that are in theme.min.css.
Making a Child Theme isn’t a difficult process once you understand how to do it. It’s basically creating a folder and a css file.
In your wp-content/themes/ folder, create a new folder called my-child-theme (or whatever you like). Inside that folder, create a file called style.css.
In style.css, put the following header, with the appropriate edits:
/*
Theme Name: my-child-theme [or whatever you want to call it]
Theme URI: https://example.com/
Description: Child theme for the [Your main Theme] theme
Author: Your name here
Author URI: https://example.com/about/
Template: twentytwelve [Put your main Theme's folder name here]
Version: 0.1.0
*/
Then, in that style.css, include the following line:
@import url("../[Main Theme's folder name]/style.css");
this will pull in the CSS from the Main (Parent) Theme
…then add your css edits and save the file.
After that, go to Appearance>Themes and activate your Child Theme.
If that doesn’t work, first check to see if your style.css is being pulled in at all (between the page’s <head> tags). If it is, then your issue is with your css.
If you still need help, I recommend checking out the Child Theme article, but if that doesn’t help, let me know.