Rename themes -> flavours ? ?

app/javascript/flavours/glitch/styles/_mixins.scss

@@ -0,0 +1,51 @@
+@mixin avatar-radius() {
+  border-radius: $ui-avatar-border-size;
+  background: transparent no-repeat;
+  background-position: 50%;
+  background-clip: padding-box;
+}
+
+@mixin avatar-size($size:48px) {
+  width: $size;
+  height: $size;
+  background-size: $size $size;
+}
+
+@mixin single-column($media, $parent: '&') {
+  .auto-columns #{$parent} {
+    @media #{$media} {
+      @content;
+    }
+  }
+  .single-column #{$parent} {
+    @content;
+  }
+}
+
+@mixin limited-single-column($media, $parent: '&') {
+  .auto-columns #{$parent}, .single-column #{$parent} {
+    @media #{$media} {
+      @content;
+    }
+  }
+}
+
+@mixin multi-columns($media, $parent: '&') {
+  .auto-columns #{$parent} {
+    @media #{$media} {
+      @content;
+    }
+  }
+  .multi-columns #{$parent} {
+    @content;
+  }
+}
+
+@mixin fullwidth-gallery {
+  &.full-width {
+    margin-left: -22px;
+    margin-right: -22px;
+    width: inherit;
+    height: 250px;
+  }
+}