Visit the following website and try out the instructions.
I was genuinely surprised and scared for a second. One can argue that this is not really a problem with terminals, but with HTML/CSS.
I don't usually copy and paste from the browser into the terminal. With longer commands I do, but only after checking the code for malicious content. After discovering this I am not sure if I can ever assume any code to be safe.
Thankfully, a user going by the username moonboots, shared the following on Hacker News:
Bash and Zsh provide shortcuts to open a text editor where commands can be pasted and edited before running (Ctrl-x Ctrl-e in bash, need to enable in zsh).
Sample .zshrc to map edit-command-line to Ctrl-x e:
autoload edit-command-line zle -N edit-command-line bindkey '^Xe' edit-command-line
So please use the aforementioned solutions for your respective shells before copy-pasting something from the web, or manually open a text editor and paste into it first.
Also remember that it's always better to just type out the commands instead of copy-pasting, though for long pieces of text it can vary from being annoying to unfeasible.