Fix: set specific border default (#5786)

**Problem:**
Today we have an empty border section in the inspector when an element doesn't have a border. This is since our code doesn't consider the computed value as "default", so it mistakenly shows the UI for them as set.
So there is no "empty state" in the border control:
<img width="302" alt="image" src="https://github.com/concrete-utopia/utopia/assets/7003853/a53eebed-9122-4c75-9ca3-281145138e0f">

**Fix:**
Set a more precise border default.

<video src="https://github.com/concrete-utopia/utopia/assets/7003853/6eaed664-10c2-4036-8216-2972a60f3818"></video>

- [X] I opened a hydrogen project and it loaded
- [X] I could navigate to various routes in Preview mode

Fixes #5752

editor/src/components/inspector/common/css-utils.ts

@@ -1040,6 +1040,33 @@ export const emptyCSSBorder: CSSBorder = {
   type: 'border',
 }
 
+export const emptyCssBorderDefault: CSSBorder = {
+  type: 'border',
+  width: {
+    type: 'line-width',
+    value: {
+      value: 0,
+      unit: 'px',
+    },
+  },
+  style: {
+    type: 'line-style',
+    value: {
+      type: 'keyword',
+      value: 'none',
+    },
+  },
+  color: {
+    type: 'RGB',
+    r: 0,
+    g: 0,
+    b: 0,
+    a: 1,
+    percentageAlpha: false,
+    percentagesUsed: false,
+  },
+}
+
 export const defaultCSSBorder: Complete<CSSBorder> = {
   type: 'border',
   style: cssLineStyle(cssKeyword('solid')),
@@ -5114,7 +5141,7 @@ export const trivialDefaultValues: ParsedPropertiesWithNonTrivial = {
   backgroundColor: cssDefault(emptyBackgroundColor),
   backgroundImage: [],
   backgroundSize: [],
-  border: emptyCSSBorder,
+  border: emptyCssBorderDefault,
   borderRadius: {
     type: 'LEFT',
     value: {

editor/src/components/inspector/sections/style-section/border-subsection/border-subsection.tsx

@@ -150,7 +150,7 @@ export const BorderSubsection: React.FunctionComponent<React.PropsWithChildren<u
       </UIGridRow>
     )
 
-    const borderSet: boolean = controlStatus !== 'unset'
+    const borderSet: boolean = controlStatus !== 'unset' && controlStatus !== 'trivial-default'
 
     const contextMenuItems = [addOnUnsetValues(['border parameters'], onUnsetValues)]