Overriding styles in BEM mixes?

Question

css

How to use mixes in BEM?
For example, I have a block with a logo, which is in both the header and the footer. In the footer, its margin differs from the margin that is set by default for the logo block. How is this supposed to work if my footer styles are higher than my logo styles?

<header class="header">
  <div class="logo">
    <img class="logo__img" src="path..." alt="logo" width="50" height="25">
  </div>
</header>

<footer class="footer">
  <div class="logo footer__logo">
    <img class="logo__img" src="path..." alt="logo" width="50" height="25">
  </div>
</footer>

.footer {
  &__logo {
    margin: 20px;
  }
}

.logo {
  margin: 10px;
}

That is, at me it is banal styles not to be redefined.
Maybe I don't understand something? Explain, please.

Answer 1

1. The block should not have a margin in principle
2. You need to use two mixes: .header__logo and .footer__logo
3. For a normal redefinition, use builds for BEM