Tweak dark theme diff highlight

The line background extension doesn't cover wrapped lines, but I don't
see an easy solution so it's fine.

Author: gavtroy

static/custom.css

@@ -153,3 +153,9 @@ pre.lang:after {
 	z-index: 5;
 	scroll-margin-top: 200px;
 }
+
+@media (min-width: 768px) {
+  .input-group {
+	max-width: 250px;
+  }
+}

static/index.html

@@ -82,8 +82,8 @@
                 <div class="ml-auto d-flex mt-1 mt-md-0 mb-1 mb-md-0">
                     {{#if (or is_editable is_created)}}
                     <div class="input-group mr-2">
-                        <div class="input-group-prepend">
-                            <button class="btn btn-outline-secondary" id="diff-button" type="button" aria-pressed="false">Diff</button>
+                        <div class="input-group-prepend" title="Diff">
+                            <button class="btn btn-outline-secondary" id="diff-button" type="button" aria-pressed="false">±</button>
                         </div>
                         <select class="form-control" id="language-selector">
                             <option value="log">Log file</option>

static/prism-coldark-pb.css

@@ -208,14 +208,15 @@ pre[class*="language-"] {
 
 /* Diff Highlight plugin overrides */
 .token.deleted {
-	color: #9c3b22;
+	color: #f4886d;
 }
 .token.inserted {
-    color: #507f3c;
+	color: #89bd73;
 }
 
 pre.diff-highlight > code .token.deleted:not(.prefix),
-pre > code.diff-highlight .token.deleted:not(.prefix) {
+pre > code.diff-highlight .token.deleted:not(.prefix),
+.token.prefix.deleted::before {
     background-color: lch(14 14 23);
 }
 
@@ -227,7 +228,8 @@ pre > code.diff-highlight .token.deleted:not(.prefix) *::selection {
 }
 
 pre.diff-highlight > code .token.inserted:not(.prefix),
-pre > code.diff-highlight .token.inserted:not(.prefix) {
+pre > code.diff-highlight .token.inserted:not(.prefix),
+.token.prefix.inserted::before {
     background-color: lch(17 18 137);
 }
 
@@ -237,3 +239,11 @@ pre > code.diff-highlight .token.inserted:not(.prefix)::selection,
 pre > code.diff-highlight .token.inserted:not(.prefix) *::selection {
     background-color: lch(23 18 137);
 }
+
+.token.prefix.inserted::before,
+.token.prefix.deleted::before {
+    content: " ";
+    display: inline-block;
+    width: 5px;
+    margin-left: -5px;
+}