[css-forms-1] Add initial UA styles for range input

Positioning of ::slider-thumb and sizing of ::slider-fill still need to be added.

Author: lukewarlow

css-forms-1/Overview.bs

@@ -816,19 +816,27 @@ select {
 ISSUE(12267): Refine meter, progress, switch and range input styling.
 
 ```css
-input[type=checkbox][switch] {
+input:is([type=checkbox][switch], [type=range]) {
   display: inline-flex;
   position: relative;
   align-items: center;
+  width: 100%;
+}
+
+input[type=checkbox][switch] {
   width: 2em;
 }
 
 ::slider-track {
   height: 1em;
+  width: 100%;
+}
+
+input[type=range]::slider-track {
+  height: 0.5em;
 }
 
 input[type=checkbox][switch]::slider-track {
-  width: 100%;
   border-radius: 1em;
 }
 
@@ -852,12 +860,8 @@ input[type=checkbox][switch]::slider-fill {
   background-color: currentColor;
   appearance: none;
   width: 1em;
-  height: 100%;
-}
-
-input[type=checkbox][switch]::slider-thumb {
-  border-radius: 100%;
   height: 1em;
+  border-radius: 100%;
   position: absolute;
 }