[Beta] Incorrect font weight

This is the current font weight of paragraphs in the beta docs

The computed styles have a font weight of 400 but it is actually 500 because there is no font face for the regular font. there is only a font face for the font of weight 500 and this can be found in index.css that only has the following font faces:

@font-face {
    font-family: 'Source Code Pro';
    font-style: normal;
    font-weight: 400;
    font-display: swap;
    src: url('/fonts/Source-Code-Pro-Regular.woff2') format('woff2');
  }

  @font-face {
    font-family: 'Optimistic Display';
    src: url('https://beta.reactjs.org/fonts/Optimistic_Display_W_Lt.woff2')
      format('woff2');
    font-weight: 300;
    font-style: normal;
    font-display: swap;
  }

  @font-face {
    font-family: 'Optimistic Display';
    src: url('https://beta.reactjs.org/fonts/Optimistic_Display_W_Md.woff2')
      format('woff2');
    font-weight: 500;
    font-style: normal;
    font-display: swap;
  }

  @font-face {
    font-family: 'Optimistic Display';
    src: url('https://beta.reactjs.org/fonts/Optimistic_Display_W_Bd.woff2')
      format('woff2');
    font-weight: 700;
    font-style: normal;
    font-display: swap;
  }

The solution would be to add a font face for the regular font because the current font weight for the paragraphs is a bit unreadable.

从 index.css 开始，检查 issue 中显示的 Optimistic Display @font-face 声明。添加缺失的 regular 字体，然后验证 beta 文档段落使用预期的 regular 字重，并且在浏览器中更易读。