Test image background (#5082)

_scss/_night-mode.scss

@@ -288,6 +288,10 @@ body.night {
     h6.dropdown-header {
         color: $white;
     }
+    /** apply to images with garbled text **/
+    img.white-bg {
+	  background-color: white;
+    }
 }
 
 

css/temp.css

@@ -7,7 +7,7 @@
 */
 
 @media print
-{    
+{
     .footer
     {
         display: none !important;

machine/overview.md

@@ -49,13 +49,13 @@ Docker Machine has these two broad use cases.
 
 * **I have an older desktop system and want to run Docker on Mac or Windows**
 
-  ![Docker Machine on Mac and Windows](img/machine-mac-win.png)
+  ![Docker Machine on Mac and Windows](img/machine-mac-win.png){: .white-bg}
 
   If you work primarily on an older Mac or Windows laptop or desktop that doesn't meet the requirements for the new [Docker for Mac](/docker-for-mac/index.md) and [Docker for Windows](/docker-for-windows/index.md) apps, then you need Docker Machine in order to "run Docker" (that is, Docker Engine) locally. Installing Docker Machine on a Mac or Windows box with the [Docker Toolbox](/toolbox/overview.md) installer provisions a local virtual machine with Docker Engine, gives you the ability to connect it, and run `docker` commands.
 
 *  **I want to provision Docker hosts on remote systems**
 
-  ![Docker Machine for provisioning multiple systems](img/provision-use-case.png)
+  ![Docker Machine for provisioning multiple systems](img/provision-use-case.png){: .white-bg}
 
   Docker Engine runs natively on Linux systems. If you have a Linux box as your
   primary system, and want to run `docker` commands, all you need to do is
@@ -91,7 +91,7 @@ on Mac or Windows) or remote (as when you use Machine to provision Dockerized
 hosts on cloud providers). The Dockerized hosts themselves can be thought of,
 and are sometimes referred to as, managed "**_machines_**".
 
-![Docker Machine](img/machine.png)
+![Docker Machine](img/machine.png){: .white-bg}
 
 ## Where to go next
 

test.md

@@ -274,6 +274,8 @@ page or displaying content as "cards".
 
 ## Jekyll / Liquid tricks
 
+### Assignment
+
 This paragraph is centered and colored green by setting CSS directly on the element.
 **Even though you can do this and it's sometimes the right way to go, remember that if
 we re-skin the site, any inline styles will need to be dealt with manually!**
@@ -296,6 +298,12 @@ You can nest captures within each other to represent more complex logic with Liq
 - In-line variables set via `assign` or `capture` are available for the remainder of the page after they are set.
 - If you include a file, you can pass key-value pairs at the same time. These are available as include variables, like `{{ include.toc_min }}`.
 
+### Image formatting
+
+This image was originally created on a white background and converted to a transparent background (or so it seems). In night-mode, the text still shows traces of the white and looks garbled. To fix this, we apply a white background inline with a class defined in _scss/_night-mode.css (and incorporated into style.css): `img.white-bg { background-color: white; }`.
+
+![alt_text](machine/img/provision-use-case.png){: .white-bg}
+
 ## Bootstrap and CSS tricks
 
 Here are cool components you can include on Docs pages using