rustdoc: clean up .out-of-band/.in-band CSS

* Remove the `float: right` fallback from the main header, which hasn't
  been needed since IE11 support was dropped.

* Remove `in-band` from low-level headers, which hasn't been needed since
  `.rightside` switched to `float: right` in
  593d6d1cb1

* Remove unreachable `.in-band > code, .in-band > .code-header` CSS, since
  the `in-band` class was attached to the `code-header` itself, not nested
  directly below it.

* Use `rem` instead of `em` for code header margins.

* This results in a slight change in spacing around impls and item-info,
  but since it makes it more consistent with the way methods are presented,
  it's probably fine.

src/librustdoc/html/render/mod.rs

@@ -1790,7 +1790,7 @@ pub(crate) fn render_impl_summary(
     write!(w, "<section id=\"{}\" class=\"impl has-srclink\"{}>", id, aliases);
     render_rightside(w, cx, &i.impl_item, containing_item, RenderMode::Normal);
     write!(w, "<a href=\"#{}\" class=\"anchor\"></a>", id);
-    write!(w, "<h3 class=\"code-header in-band\">");
+    write!(w, "<h3 class=\"code-header\">");
 
     if let Some(use_absolute) = use_absolute {
         write!(w, "{}", inner_impl.print(use_absolute, cx));

src/librustdoc/html/static/css/rustdoc.css

@@ -176,8 +176,8 @@ h4.code-header {
 	border-bottom-style: none;
 	margin: 0;
 	padding: 0;
-	margin-top: 0.6em;
-	margin-bottom: 0.4em;
+	margin-top: 0.6rem;
+	margin-bottom: 0.4rem;
 }
 .impl,
 .impl-items .method,
@@ -658,18 +658,17 @@ h2.location a {
 	overflow-x: auto;
 }
 
-.content .out-of-band {
+.out-of-band {
 	flex-grow: 0;
 	font-size: 1.125rem;
 	font-weight: normal;
-	float: right;
 }
 
 .method > .code-header, .trait-impl > .code-header {
 	display: block;
 }
 
-.content .in-band {
+.in-band {
 	flex-grow: 1;
 	margin: 0px;
 	padding: 0px;
@@ -682,10 +681,6 @@ h2.location a {
 	background-color: var(--main-background-color);
 }
 
-.in-band > code, .in-band > .code-header {
-	display: inline-block;
-}
-
 .docblock code, .docblock-short code,
 pre, .rustdoc.source .example-wrap {
 	background-color: var(--code-block-background-color);
@@ -1731,13 +1726,13 @@ in storage.js plus the media query with (min-width: 701px)
 		flex-direction: column;
 	}
 
-	.content .out-of-band {
+	.out-of-band {
 		text-align: left;
 		margin-left: initial;
 		padding: initial;
 	}
 
-	.content .out-of-band .since::before {
+	.out-of-band .since::before {
 		content: "Since ";
 	}
 
@@ -1969,7 +1964,7 @@ in storage.js plus the media query with (min-width: 701px)
 }
 
 @media print {
-	nav.sidebar, nav.sub, .content .out-of-band, a.srclink, #copy-path,
+	nav.sidebar, nav.sub, .out-of-band, a.srclink, #copy-path,
 	details.rustdoc-toggle[open] > summary::before, details.rustdoc-toggle > summary::before,
 	details.rustdoc-toggle.top-doc > summary {
 		display: none;

src/librustdoc/html/static/js/main.js

@@ -555,7 +555,6 @@ function loadCss(cssFileName) {
                 const code = document.createElement("h3");
                 code.innerHTML = struct[TEXT_IDX];
                 addClass(code, "code-header");
-                addClass(code, "in-band");
 
                 onEachLazy(code.getElementsByTagName("a"), elem => {
                     const href = elem.getAttribute("href");

src/test/rustdoc-gui/headers-color.goml

@@ -19,7 +19,7 @@ assert-css: (
 )
 assert-css: (
     ".impl .code-header",
-    {"color": "rgb(230, 225, 207)", "background-color": "rgb(15, 20, 25)"},
+    {"color": "rgb(230, 225, 207)", "background-color": "rgba(0, 0, 0, 0)"},
     ALL,
 )
 
@@ -58,7 +58,7 @@ assert-css: (
 )
 assert-css: (
     ".impl .code-header",
-    {"color": "rgb(221, 221, 221)", "background-color": "rgb(53, 53, 53)"},
+    {"color": "rgb(221, 221, 221)", "background-color": "rgba(0, 0, 0, 0)"},
     ALL,
 )
 
@@ -95,7 +95,7 @@ assert-css: (
 )
 assert-css: (
     ".impl .code-header",
-    {"color": "rgb(0, 0, 0)", "background-color": "rgb(255, 255, 255)"},
+    {"color": "rgb(0, 0, 0)", "background-color": "rgba(0, 0, 0, 0)"},
     ALL,
 )
 

src/test/rustdoc-gui/implementors.goml

@@ -8,23 +8,23 @@ assert-count: ("#implementors-list .impl", 2)
 assert: ("#implementors-list .impl:nth-child(1) > a.anchor")
 assert-attribute: ("#implementors-list .impl:nth-child(1)", {"id": "impl-Whatever-for-Struct"})
 assert-attribute: ("#implementors-list .impl:nth-child(1) > a.anchor", {"href": "#impl-Whatever-for-Struct"})
-assert: "#implementors-list .impl:nth-child(1) > .code-header.in-band"
+assert: "#implementors-list .impl:nth-child(1) > .code-header"
 
 assert: ("#implementors-list .impl:nth-child(2) > a.anchor")
 assert-attribute: ("#implementors-list .impl:nth-child(2)", {"id": "impl-Whatever-1"})
 assert-attribute: ("#implementors-list .impl:nth-child(2) > a.anchor", {"href": "#impl-Whatever-1"})
-assert: "#implementors-list .impl:nth-child(2) > .code-header.in-band"
+assert: "#implementors-list .impl:nth-child(2) > .code-header"
 
 goto: file://|DOC_PATH|/test_docs/struct.HasEmptyTraits.html
 compare-elements-position-near-false: (
     "#impl-EmptyTrait1-for-HasEmptyTraits",
     "#impl-EmptyTrait2-for-HasEmptyTraits",
-    {"y": 30},
+    {"y": 34.1875},
 )
 compare-elements-position-near: (
     "#impl-EmptyTrait3-for-HasEmptyTraits h3",
     "#impl-EmptyTrait3-for-HasEmptyTraits .item-info",
-    {"y": 30},
+    {"y": 34.1875},
 )
 
 // Now check that re-exports work correctly.

src/test/rustdoc-gui/src-font-size.goml

@@ -5,7 +5,7 @@ goto: file://|DOC_PATH|/test_docs/struct.Foo.html
 show-text: true
 // Check the impl headers.
 assert-css: (".impl.has-srclink .srclink", {"font-size": "16px"}, ALL)
-assert-css: (".impl.has-srclink .code-header.in-band", {"font-size": "18px"}, ALL)
+assert-css: (".impl.has-srclink .code-header", {"font-size": "18px"}, ALL)
 // Check the impl items.
 assert-css: (".impl-items .has-srclink .srclink", {"font-size": "16px"}, ALL)
 assert-css: (".impl-items .has-srclink .code-header", {"font-size": "16px"}, ALL)