feat(mixin): add mixins and common placeholders

.scss-lint.yml

@@ -0,0 +1,81 @@
+severity: error
+
+files:
+  include:
+    - 'src/**/*.s+(a|c)ss'
+  ignore:
+    - 'node_modules/**/*.s+(a|c)ss'
+    - 'test/**/*.s+(a|c)ss'
+
+rules:
+  indentation:
+    - 2
+    -
+      size: 4
+
+  class-name-format:
+    - 1
+    - convention: '([a-z0-9_]+-?)+'
+
+  mixin-name-format:
+    - 1
+    - convention: '([a-z0-9_]+-?)+'
+
+  placeholder-name-format:
+    - 1
+    - convention: '([a-z0-9_]+-?)+'
+
+  variable-name-format:
+    - 1
+    - convention: '([a-z0-9]+-?)+'
+
+  space-before-brace:
+    - 2
+
+  no-important:
+    - 2
+
+linters:
+
+  BorderZero:
+    enabled: true
+    convention: zero
+
+  BemDepth:
+    enabled: true
+
+  DeclarationOrder:
+    enabled: false
+
+  ExtendDirective:
+    enabled: true
+
+  LeadingZero:
+    enabled: false
+
+  NameFormat:
+    enabled: true
+
+  PrivateNamingConvention:
+    enabled: true
+    prefix: _
+
+  PropertySortOrder:
+    enabled: false
+
+  QualifyingElement:
+    enabled: false
+
+  SelectorFormat:
+    enabled: true
+    convention: hyphenated_BEM
+    class_convention: ^(?!js-).*
+    class_convention_explanation: should not be written in the form js-*
+
+  SingleLinePerProperty:
+    enabled: true
+    allow_single_line_rule_sets: false
+
+  StringQuotes:
+    enabled: true
+    style: double_quotes

src/dynamic/libs/_common.scss

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+%background-cover {
+    background-position: 50% 50%;
+    background-repeat: no-repeat;
+    background-size: cover;
+}

src/dynamic/libs/_overs.scss

@@ -0,0 +1,3 @@
+%hover-theme--duke {
+    display: block;
+}