fix(CSS): correct multiple CSS issues w/ ShadyDOM

Closes #183
Closes #184
Closes #185

Author: Ryan A. Johnson

src/helix-ui/elements/_hx-modal.less

@@ -18,6 +18,7 @@
 }
 
 #close {
+  background-color: transparent;
   border: none;
   color: @gray-700;
   cursor: pointer;

src/helix-ui/styles/core/hx-modal.less

@@ -31,7 +31,7 @@ hx-modal {
     flex-direction: column;
   }
 
-  > hx-modalhead {
+  hx-modalhead {
     flex-shrink: 0;
     order: 1;
 
@@ -40,7 +40,7 @@ hx-modal {
     }
   }
 
-  > hx-modalbody {
+  hx-modalbody {
     flex-grow: 1;
     order: 2;
 
@@ -49,7 +49,7 @@ hx-modal {
     }
   }
 
-  > hx-modalfoot {
+  hx-modalfoot {
     flex-shrink: 0;
     order: 3;
   }

src/helix-ui/styles/modules/stepper.less

@@ -11,7 +11,7 @@ hx-accordion.beta-hxStepper {
       border-bottom: 1px solid @gray-300;
     }
 
-    > header[slot="header"] {
+    header[slot="header"] {
       display: flex;
       padding: 1rem;