Make subject field stand out like to and cc

Is your feature request related to a problem? Please describe.

The subject part when composing a new mail looks very much like a heading. I, and others I work with, find themself forgetting to set a subject and start typing the mail body. Only to realise when pressing 'send' that the subject was forgotten. Luckily, there is a warning for this.

Describe the solution you'd like

Perhaps make the subject look like an actual input:

Describe alternatives you've considered

For now, I've added custom CSS:

.message-composer .composer-fields #subject {
    border: 1px solid rgb(125, 125, 125) !important;
    border-radius: 8px !important;
    padding-left: 10px !important;
    padding-right: 10px !important;
}

Additional context

Using

Mail Version 5.10.11