SCSS support tools

Signed-off-by: Valentin Popov <info@valentineus.link>

_scss/utilities/_boxsizing.scss

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+// Box Sizing
+//
+// The box-sizing property in CSS controls how the box model
+// is handled for the element it applies to.
+//
+// Values: content-box | border-box
+// Default: content-box
+//
+// https://www.w3.org/TR/css-ui-3/#box-sizing
+@mixin box-sizing($value: content-box) {
+  -webkit-box-sizing: $value;
+     -moz-box-sizing: $value;
+      -ms-box-sizing: $value;
+          box-sizing: $value;
+}

_scss/utilities/_textsizeadjust.scss

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+// Text Size Adjust
+//
+// The text-size-adjust CSS property controls the text inflation algorithm used on some smartphones and tablets. Other browsers will ignore this property.
+//
+// Values: none | auto | <percentage>
+// Default: none
+//
+// https://drafts.csswg.org/css-size-adjust/#adjustment-control
+@mixin text-size-adjust($value: none) {
+  -webkit-text-size-adjust: $value;
+     -moz-text-size-adjust: $value;
+      -ms-text-size-adjust: $value;
+}