msglist: Make padding and margin independent of font size.

Change the units used for padding and margins from 'rem' to 'px'.
This makes these UI elements not scale with font size change.

While this would be undesirable from a purely designer's point of view,
and not something we would do for a web app, that is a best practice
that the tested apps follow on mobile.  This leaves more space for
the text when enlarged, considering the limited space.

[greg: separated small changes of actual lengths into an explicit
 preceding commit; cleaned out some noise of unrelated other changes]

src/webview/css/css.js

@@ -29,11 +29,11 @@ p {
 code {
   font-size: .857rem;
   white-space: pre-wrap;
-  padding: 0 0.25rem;
+  padding: 0 4px;
 }
 pre {
-  padding: 0.5rem;
-  margin: 0.5rem 0;
+  padding: 8px;
+  margin: 8px 0;
   font-size: 0.75rem;
   white-space: pre;
   overflow-x: auto;
@@ -57,10 +57,10 @@ thead {
 }
 th, td {
   align: center;
-  padding: 0.25rem 0.5rem;
+  padding: 4px 8px;
 }
 hr {
-  margin: 1rem 0;
+  margin: 16px 0;
   border: 0;
   border-top: 1px solid rgba(127, 127, 127, 0.5);
 }
@@ -74,20 +74,20 @@ hr {
   display: flex;
   flex-direction: row;
   justify-content: space-between;
-  margin-bottom: 0.25rem;
+  margin-bottom: 4px;
 }
 .timerow {
   text-align: center;
   color: #999;
   display: flex;
   align-items: center;
-  padding: 0.5rem 0;
+  padding: 8px 0;
 }
 .timerow-left,
 .timerow-right {
   flex: 1;
   height: 1px;
-  margin: 0.5rem;
+  margin: 8px;
 }
 .timerow-left {
   background: -webkit-linear-gradient(left, transparent 10%, #999 100%);
@@ -104,20 +104,20 @@ hr {
 .loading {
   display: flex;
   word-wrap: break-word;
-  padding: 1rem;
+  padding: 16px;
 }
 .message-brief {
-  padding: 0 1rem 1rem 4rem;
+  padding: 0 16px 16px 64px;
 }
 .message p + p {
-  margin-top: 1rem;
+  margin-top: 16px;
 }
 .avatar,
 .loading-avatar {
   min-width: 32px;
   width: 32px;
   height: 32px;
-  margin-right: 1rem;
+  margin-right: 16px;
 }
 .avatar img {
   width: 100%;
@@ -139,7 +139,7 @@ hr {
   white-space: nowrap;
   background-color: rgba(0, 0, 0, 0.1);
   border-radius: 3px;
-  padding: 0 .125rem;
+  padding: 0 2px;
   box-shadow: 0 0 0 1px rgba(0, 0, 0, 0.2);
 }
 .header-wrapper {
@@ -166,7 +166,7 @@ hr {
   white-space: nowrap;
 }
 .private-header {
-  padding: 0 0.5rem;
+  padding: 0 8px;
 }
 .topic-header {
   background: #ccc;
@@ -250,7 +250,7 @@ hr {
   width: 2rem;
   height: 2rem;
   border-radius: 50%;
-  margin: 1rem auto;
+  margin: 16px auto;
   font-size: 10px;
   border: 3px solid rgba(82, 194, 175, 0.25);
   border-left: 3px solid rgba(82, 194, 175, 0.75);
@@ -274,16 +274,16 @@ hr {
   object-fit: contain;
 }
 blockquote {
-  padding-left: 0.5rem;
-  margin: 0.5rem 0 0.5rem 0;
+  padding-left: 8px;
+  margin: 8px 0 8px 0;
   border-left: 3px solid rgba(127, 127, 127, 0.5);
 }
 .message ul {
-  padding-left: 1.25rem;
-  margin: 0.25rem 0 0 0;
+  padding-left: 20px;
+  margin: 4px 0 0 0;
 }
 .message ul + p {
-  margin-top: 1rem;
+  margin-top: 16px;
 }
 .codehilite .gi { color: #00a000; }
 .codehilite .gd { color: #a00000; }
@@ -300,34 +300,34 @@ blockquote {
   border: 2px solid rgba(29, 161, 242, 0.5);
   background: rgba(29, 161, 242, 0.1);
   border-radius: 6px;
-  padding: 0.5rem 1rem;
-  margin: 0.5rem 0;
+  padding: 8px 16px;
+  margin: 8px 0;
 }
 .twitter-avatar {
   border-radius: 3px;
-  margin: 0.5rem 0.5rem 0.25rem 0;
+  margin: 8px 8px 4px 0;
   float: left;
   width: 2.2rem;
   height: 2.2rem;
 }
 .twitter-image {
   text-align: center;
-  margin: 0.5rem auto;
+  margin: 8px auto;
 }
 .message-tags {
   text-align: right;
-  margin: 0.25rem 0;
+  margin: 4px 0;
   font-size: 0.7rem;
 }
 .message-tag {
-  padding: 0.25rem 0.25rem;
-  margin-left: 4;
+  padding: 4px 4px;
+  margin-left: 4px;
   border-radius: 3px;
   color: rgba(127, 127, 127, 0.75);
   background: rgba(0, 0, 0, 0.1);
 }
 .reaction-list {
-  margin: 0.5rem 0;
+  margin: 8px 0;
 }
 .reaction {
   color: rgba(127, 127, 127, 1);
@@ -337,7 +337,7 @@ blockquote {
   border: 1px solid rgba(127, 127, 127, 0.75);
   line-height: 1rem;
   height: 1rem;
-  margin: .25rem 0.5rem .25rem 0;
+  margin: 4px 8px 4px 0;
 }
 .reaction img {
   pointer-events: none;
@@ -377,11 +377,11 @@ blockquote {
 }
 #typing {
   display: flex;
-  padding-left: 1rem;
+  padding-left: 16px;
 }
 #typing .content {
-  padding-top: 0.5rem;
-  padding-bottom: 1rem;
+  padding-top: 8px;
+  padding-bottom: 16px;
 }
 #typing span {
   display: inline-block;