Consistently format CSS color and opacity values

- Prefer the modern comma-free CSS color function syntax over the
  legacy syntax. [1]
- Explicitly use the `deg` suffix for angle values in colors, to
  clarify the range.
- Explicitly use the `%` suffix for percentages instead of formatting
  the value as a number, again to clarify the range.

[1]: https://twitter.com/mathias/status/1253242715304857601
[2]: https://goo.gle/devtools-css-color

Bug: chromium:1083142
Fixed: chromium:1073885
Change-Id: I8e1582a2dee3553a61df88564051ea84c2011d76
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2209091
Reviewed-by: Alex Rudenko <[email protected]>
Reviewed-by: Tim van der Lippe <[email protected]>
Commit-Queue: Tim van der Lippe <[email protected]>
Auto-Submit: Mathias Bynens <[email protected]>
diff --git a/front_end/ui/checkboxTextLabel.css b/front_end/ui/checkboxTextLabel.css
index 20b45b3..9214041 100644
--- a/front_end/ui/checkboxTextLabel.css
+++ b/front_end/ui/checkboxTextLabel.css
@@ -30,9 +30,9 @@
 input.dt-checkbox-themed {
   -webkit-appearance: none;
   margin: auto 5px auto 2px;
-  border: 1px solid rgb(45, 45, 45);
+  border: 1px solid rgb(45 45 45);
   border-radius: 3px;
-  background-color: rgb(102, 102, 102);
+  background-color: rgb(102 102 102);
 }
 
 input.dt-checkbox-themed::after {