Open a text editor, paste the above snippet and save it as hiddentags.css (or whatever file name you want to chose - only the .css is important!). In your vault, there should be a folder .obsidian/snippets - save your file in this folder.
After that, in obsidian, open the app’s settings, navigate to “appearance” and activate your file under “css snippets” (if it doesn’t appear there, chose “reload snippets”).
If you want to hide several tags, paste the above code multiple times in your newly created file and replace the #date with the tags you want to be hidden, for example
a.tag[href="#event"] {
display: none;
}