Paint media element's play button using padding.

third_party/WebKit/Source/core/css/mediaControlsNew.css

 /*
  * Copyright (C) 2009 Apple Inc.  All rights reserved.
  * Copyright (C) 2015 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 15 matching lines @@
 /* Chromium default media controls */
 
 /* WARNING: This css file can only style <audio> and <video> elements */
 
 audio:not([controls]) {
     display: none !important;
 }
 
 audio {
     width: 300px;
-    height: 48px;
+    height: 32px;
 }
 
 audio::-webkit-media-controls,
 video::-webkit-media-controls {
     width: inherit;
     height: inherit;
     position: relative;
     direction: ltr;
     display: flex;
     flex-direction: column;
     justify-content: flex-end;
     align-items: center;
 }
 
 audio::-webkit-media-controls-enclosure, video::-webkit-media-controls-enclosure {
     width: 100%;
-    height: 48px;
+    height: 32px;
     flex-shrink: 0;
     bottom: 0;
     text-indent: 0;
     padding: 0;
     margin: 0;
     box-sizing: border-box;
 }
 
 audio::-webkit-media-controls-panel, video::-webkit-media-controls-panel {
     display: flex;
     flex-direction: row;
     align-items: center;
     /* We use flex-start here to ensure that the play button is visible even
      * if we are too small to show all controls.
      */
     justify-content: flex-start;
     -webkit-user-select: none;
     position: relative;
     width: 100%;
     z-index: 0;
     overflow: hidden;
     text-align: right;
     bottom: auto;
-    height: 48px;
+    height: 32px;
     min-width: 48px;
+    line-height: 32px;
     background-color: #fafafa;
     /* The duration is also specified in MediaControlElements.cpp and LayoutTests/media/media-controls.js */
     transition: opacity 0.3s;
 
     font-family: Segoe, "Helvetica Neue", Roboto, Arial, Helvetica, sans-serif ;
-    font-size: 14px;
+    font-size: 12px;
     font-weight: normal;  /* Make sure that we don't inherit non-defaults. */
     font-style: normal;
 }
 
 video:-webkit-full-page-media {
     margin: auto;
     position: absolute;
     top: 0;
     right: 0;
     bottom: 0;
     left: 0;
 }
 
 audio:-webkit-full-page-media, video:-webkit-full-page-media {
     max-height: 100%;
     max-width: 100%;
 }
 
 audio:-webkit-full-page-media::-webkit-media-controls-panel,
 video:-webkit-full-page-media::-webkit-media-controls-panel {
     bottom: 0px;
 }
 
 audio::-webkit-media-controls-mute-button, video::-webkit-media-controls-mute-button {
     -webkit-appearance: media-mute-button;
     display: flex;
     flex: none;
-    border: none;
-    width: 48px;
-    height: 48px;
-    line-height: 48px;
-    padding: 12px;
+    box-sizing: content-box;
+    width: 32px;
+    height: 32px;
+    padding: 0px;
+    border-width: 0px;
     background-color: initial;
     color: inherit;
 }
 
 audio::-webkit-media-controls-overlay-enclosure {
     display: none;
 }
 
 video::-webkit-media-controls-overlay-enclosure {
     display: flex;
@@ skipping 11 matching lines @@
     overflow: hidden;
 }
 
 video::-webkit-media-controls-overlay-play-button {
     -webkit-appearance: media-overlay-play-button;
     display: flex;
     position: absolute;
     top: 0;
     left: 0;
     margin: 0;
-    border: none;
+    border-width: 0px;

[philipj_slow, 2016/04/01 08:47:31]

A pet peeve of mine: 0px==0. There are a bunch of existing cases in this file,
so if you want to fix them all that'd be nice.

     background-color: transparent;
     width: 100%;
     height: 100%;
     padding: 0;
 }
 
 video::-internal-media-controls-overlay-cast-button {
     -webkit-appearance: -internal-media-overlay-cast-off-button;
     display: flex;
     position: absolute;
     top: 8px;
     left: 8px;
     margin-left: 0px;
     margin-top: 0px;
-    border: none;
+    border-width: 0px;
     background-color: transparent;
-    width: 48px;
-    height: 48px;
+    width: 32px;
+    height: 32px;
     padding: 0;
     transition: opacity 0.3s;
 }
 
 audio::-webkit-media-controls-play-button, video::-webkit-media-controls-play-button {
     -webkit-appearance: media-play-button;
     display: flex;
     flex: none;
-    border-sizing: border-box;
-    width: 48px;
-    height: 48px;
-    line-height: 48px;
-    padding: 12px;
+    box-sizing: content-box;
+    width: 32px;
+    height: 32px;
+    padding: 0px;
+    border-width: 0px;
     background-color: initial;
     color: inherit;
 }
 
 audio::-webkit-media-controls-timeline-container, video::-webkit-media-controls-timeline-container {
     -webkit-appearance: media-controls-background;
     display: flex;
     flex-direction: row;
     align-items: center;
     justify-content: flex-end;
     flex: 1 1;
     -webkit-user-select: none;
     height: 48px;
     padding: 0;
     min-width: 0;
 }
 
 audio::-webkit-media-controls-current-time-display, video::-webkit-media-controls-current-time-display {
     -webkit-appearance: media-current-time-display;
     -webkit-user-select: none;
     flex: none;
     display: flex;
     border: none;
     cursor: default;
 
-    height: 48px;
+    height: 32px;
 
     /* text runs right to the edge of the container */
     padding: 0;
 
-    line-height: 48px;
     color: #5a5a5a;
 
     letter-spacing: normal;
     word-spacing: normal;
     text-transform: none;
     text-indent: 0;
     text-shadow: none;
     text-decoration: none;
 }
 
 audio::-webkit-media-controls-time-remaining-display, video::-webkit-media-controls-time-remaining-display {
     -webkit-appearance: media-current-time-display;
     -webkit-user-select: none;
     flex: none;
     display: flex;
     border: none;
     cursor: default;
 
-    height: 48px;
+    height: 32px;
 
     /* text runs right to the edge of the container, plus a little on
      * the left to pad the leading "/" */
     padding: 0 0 0 4px;
 
-    line-height: 48px;
     color: #5a5a5a;
 
     letter-spacing: normal;
     word-spacing: normal;
     text-transform: none;
     text-indent: 0;
     text-shadow: none;
     text-decoration: none;
 }
 
@@ skipping 61 matching lines @@
     width: 48px;
     height: 48px;
     padding: 0px;
 }
 
 audio::-webkit-media-controls-fullscreen-button, video::-webkit-media-controls-fullscreen-button {
     -webkit-appearance: media-enter-fullscreen-button;
     display: flex;
     flex: none;
     overflow: hidden;
-    border: none;
-    width: 48px;
-    height: 48px;
-    line-height: 48px;
+    box-sizing: content-box;
+    width: 32px;
+    height: 32px;
+    padding: 0px;
+    border-width: 0px;
     background-color: initial;
     color: inherit;
 }
 
 audio::-internal-media-controls-cast-button, video::-internal-media-controls-cast-button {
     -webkit-appearance: -internal-media-cast-off-button;
     display: flex;
     flex: none;
-    border: none;
-    width: 48px;
-    height: 48px;
-    line-height: 48px;
+    box-sizing: content-box;
+    width: 32px;
+    height: 32px;
+    padding: 0px;
+    border-width: 0px;
     margin-left: 0px;
     margin-right: 0px;
-    padding: 12px;
     background-color: initial;
     color: inherit;
 }
 
 audio::-webkit-media-controls-toggle-closed-captions-button {
     display: none;
 }
 
 video::-webkit-media-controls-toggle-closed-captions-button {
     -webkit-appearance: media-toggle-closed-captions-button;
     display: flex;
     flex: none;
-    border: none;
-    width: 48px;
-    height: 48px;
-    line-height: 48px;
+    box-sizing: content-box;
+    width: 32px;
+    height: 32px;
+    padding: 0px;
+    border-width: 0px;
     margin-left: 0px;
     margin-right: 0px;
-    padding: 12px;
     background-color: initial;
     color: inherit;
 }
 
 audio::-webkit-media-controls-fullscreen-volume-slider, video::-webkit-media-controls-fullscreen-volume-slider {
     display: none;
 }
 
 audio::-webkit-media-controls-fullscreen-volume-min-button, video::-webkit-media-controls-fullscreen-volume-min-button {
     display: none;
@@ skipping 70 matching lines @@
     font-weight: bold;
 }
 
 video::cue(u) {
     text-decoration: underline;
 }
 
 video::cue(i) {
     font-style: italic;
 }