Add USA header to base templates

styles/atat.scss

@@ -36,6 +36,7 @@
 @import 'components/selector';
 @import 'components/budget_chart';
 @import 'components/audit_log';
+@import 'components/usa_banner';
 
 @import 'sections/login';
 @import 'sections/request_approval';

styles/components/_usa_banner.scss

@@ -0,0 +1,27 @@
+.usa-banner {
+  display: flex;
+  align-items: center;
+  padding: ($gap / 2) $gap;
+  z-index: 5;
+
+  img {
+    flex-grow: 0;
+    margin-right: $gap;
+  }
+
+  p {
+    margin: 0;
+  }
+
+  button.icon-tooltip {
+    @include small-label;
+    color: $color-blue;
+    padding: 0 ($gap / 2);
+    margin: 0 ($gap / 2);
+    font-weight: normal;
+
+    .icon {
+      @include icon-size(12);
+    }
+  }
+}