Add supporting themes required for Lotusdocs

themes/twbs/bootstrap/scss/mixins/_resize.scss

@@ -0,0 +1,6 @@
+// Resize anything
+
+@mixin resizable($direction) {
+  overflow: auto; // Per CSS3 UI, `resize` only applies when `overflow` isn't `visible`
+  resize: $direction; // Options: horizontal, vertical, both
+}