added cactus theme files

hugo-content/themes/cactus/assets/scss/_mixins.scss

@@ -0,0 +1,20 @@
+@mixin antialias() {
+  -moz-osx-font-smoothing: grayscale;
+  -webkit-font-smoothing: antialiased;
+}
+@mixin hyphens($value) {
+  hyphens: $value;
+  -moz-hyphens: $value;
+  -ms-hyphens: $value;
+  -webkit-hyphens: $value;
+}
+@mixin underline($size, $color) {
+  background-image: linear-gradient(transparent, transparent $size, $color $size, $color);
+  background-position: bottom;
+  background-size: 100% 6px;
+  background-repeat: repeat-x;
+}
+@mixin no-select() {
+  user-select: none;
+  -khtml-user-select: none;
+}