<button class="blue text font-size hover round-btn margin-full">
  Button
</button>

<button class="bg-blue-500 text-white font-bold py-2 px-4 rounded-full hover:bg-blue-700">
  Button
</button>

<button class="set-blue set-text set-font set-hover round-btn padding-full">
  Button
</button>

<button class="color-blue text-color font-size allow-hover round-btn">
  Button
</button>

?primary-color: #3498eb;

header {
  background-color: ?primary-color;
}

>primary-color: #3498eb;

header {
  background-color: >primary-color;
}

#primary-color: #3498eb;

header {
  background-color: #primary-color;
}

@mixin center-flex {
  display: flex;
  justify-content: center;
  align-items: center;
}

mixin center-flex {
  display: flex;
  justify-content: center;
  align-items: center;
}

--mixin center-flex {
  display: flex;
  justify-content: center;
  align-items: center;
}

>mixin center-flex {
  display: flex;
  justify-content: center;
  align-items: center;
}