[HANDS-ON BUG] Text not clearly visible with <iframe>

**Describe the bug**
In the unit of [What are LLMs](https://huggingface.co/learn/agents-course/en/unit1/what-are-llms#what-is-a-large-language-model), there is this Tokenizer Playground where user can input their own sentences and it will display the tokens.

The generated text from the second text field is not easily visible, especially when the user selects Token IDs. From my perspective, the text field background is white in color, and the text is also white in color.

I'm not sure if this is due to the fact that I'm using dark mode.

**To Reproduce**
Type in any text into the Tokenizer Playground, and the result's text field will show white text on white background.

**Screenshots**


I'll have to specifically highlight the text to see it clearly.


**Additional context**
N/A