How do I use jade(pug)'s "if statement" inside a css block?

Say I have a jade template like:

style.
  .someclass1{
    font-size:10px;
  }
  .someclass2{
    font-size:10px;
  }
  .someclass3{
    font-size:10px;
  }
  .someclass4{
    font-size:10px;
  }
  .someclass5{
    font-size:10px;
  }

And I want to make .someclass3 with different results from different options when rendering the jade template.

Something like:

style.
  .someclass1{
    font-size:10px;
  }
  .someclass2{
    font-size:10px;
  }
  if(options.key1=='a')
    .someclass3{
      font-size:10px;
    }
  else
    .someclass3{
      font-size:8px;
    }
  .someclass4{
    font-size:10px;
  }
  .someclass5{
    font-size:10px;
  }

It's not working.

I have to break the style tag into two and do something like this:

style.
  .someclass1{
    font-size:10px;
  }
  .someclass2{
    font-size:10px;
  }
if(options.key1=='a')
  style.
    .someclass3{
      font-size:10px;
    }
else
  style.
    .someclass3{
      font-size:8px;
    }
style.
  .someclass4{
    font-size:10px;
  }
  .someclass5{
    font-size:10px;
  }

This will result in a 3-style tags HTML, which is actually only needing one.

Anyone has good way to do this?

You can do this. Instead of putting the . immediately after the style tag (which tells pug that the entire block is plain text), you can put the . before each block of plain text. eg.

style
  .
    .someclass1{
      font-size:10px;
    }
    .someclass2{
      font-size:10px;
    }
  if options.key1=='a'
    .
      .someclass3{
        font-size:10px;
      }
  else
    .
      .someclass3{
        font-size:8px;
      }
  .
    .someclass4{
      font-size:10px;
    }
    .someclass5{
      font-size:10px;
    }