Define Style coding convention

[josix]

As discussed in the meeting, we would like to have a rule of coding convention about writing styles.
Please help create a document about the practice of writing CSS style attached with the created PRs as an example for reference.
I think the below points need to be emphasized, please feel free to add it if there are other concerns.

• Writing inline style as first option, and write class alternatively if the style is not supported by tailwindcss.
• If there exists duplicated css style in the common HTML structure, please consider extracting it as another component with unified style definitions.
• The content in i18n should be limited to items that require translation. Unrelated content such as external links, icons should be avoided. PR#395 is an example of this.
• Comments should only be added to code that contains useful information for programming. Avoid adding comments to code that is uncertain or about to be deleted.
• The code files related to the schedule page are good examples that follow the above points.