Added Masthead, CMDPalette and PostHeader Components

src/styles/mixins/grid.css

@@ -0,0 +1,19 @@
+@define-mixin grid-col $col, $spacing {
+  display: grid;
+  grid-template-columns: repeat($col, minmax(0, 1fr));
+  gap: $spacing;
+}
+
+@define-mixin grid-rows $row, $spacing {
+  display: grid;
+  grid-template-rows: repeat(1, minmax(0, 1fr));
+  gap: $spacing;
+}
+
+@define-mixin grid-col-span $span {
+  grid-column: span $span / span $span;
+}
+
+@define-mixin grid-row-span $span {
+  grid-row: span $span / span $span;
+}