Regrettably, these websites come with numerous limitations. One potential solution is to utilize the recommended platforms for compressing your css and html code. Although it may significantly reduce readability, it will enable you to accommodate a larger amount of characters.
For css for html
If this approach proves unsuccessful, you might need to edit certain segments of your code in order to meet their requirements. Give those websites a try by simply copying and pasting your codes; they will generate the compressed version which you can then paste into the e-commerce portal. Opt for 'most compressed/ 0 readability' if prompted to maximize compression.
UPDATE : Based on your feedback, it seems that even utilizing the body tag is not permitted as per their guidelines. Could you please share the specific rules of the website?
UPDATE 2: Notably, there are no explicit directives indicating a requirement for a css code. The primary focus revolves around structuring a well-crafted html code for the product description and marketing content. Your product description should adhere to a strict limit of 420 characters, exclusively text-based. Conversely, the marketing description allows inclusion of images while maintaining a maximum character count of 5000. Omitting a css code submission appears to be the reason behind your current inability to proceed.