example.scss

.booking-content-wrapper {
    position: relative;
    min-height: 15rem;
    padding: 0 0 3rem;

    @include theme($laColeccion $grandFiestaAmericana) {
      color: #fff;
      &::before {
        position: absolute;
        top: -1rem;
        bottom: 0;
        left: auto;
        right: 0;
        width: 100vw;
        content: '';
      }
    }

    @include theme($laColeccion) {
      &::before {
        background: $primary-theme-color;
      }
    }

    @include theme($grandFiestaAmericana) {
      &::before {
        background: $secondary-theme-color;
      }
    }
  }

mixin-themes.scss

@function contains($list, $item) {
  @return not not index($list, $item);
}

@mixin theme($themeList) {
  @if contains($themeList, $currentTheme) {
    @content;
  }
}

theme-settings.scss

$fiestaAmericana: 'fiesta-americana';
$laColeccion: 'la-coleccion';
$grandFiestaAmericana: 'grand-fiesta-americana';
$liveAqua: 'live-aqua';
$fiestaRewards: 'fiesta-awards';
$viaja: 'viaja';
$fiestaInn: 'fiesta-inn';
$gamma: 'gamma';
$one: 'one';

variables.scss

// SCSS variables
$pathAsset: '~app';
$pathFont: 'font';
$max-width-full: 166rem;
$max-width: 136.6rem;
$z-index: default, content, destination-module, header, brand-selector, popup;

@import 'theme-settings';
// @import 'theme/live-aqua';
// @import 'theme/fiesta-americana';
// @import 'theme/grand-fiesta-americana';
// @import 'theme/la-coleccion';
@import 'theme/viaja';

viaja.scss

@import url('https://fonts.googleapis.com/css?family=Roboto&display=swap');

$colorList: #0096ff #3c457d #f8cf40 #474f57;
$fontList: 'Avenir Next', 'Roboto', 'Roboto';

$font-primary: nth($fontList, 1), sans-serif;
$font-secondary: nth($fontList, 2), sans-serif;
$font-base: nth($fontList, 3), sans-serif;

$primary-theme-color: nth($colorList, 1);
$primary-theme-color-light: nth($colorList, 2);
$secondary-theme-color: nth($colorList, 3);
$error-color: nth($colorList, 4);
$color-dark-gray: #666;

$currentTheme: $viaja;