You can adjust the background color setting and size of the default subtitles directly from your watching device. Please see below for the direction:
Subtitle Background
Windows 10 & above
1. Click Start on your laptop/computer, go to Start → Settings → Ease of Access → Closed captioning
2. Set the Caption color you like according to your preferences (if you want the background of the subtitle to be transparent, you can set the Caption background transparency to 0%)
3. Close the Chrome browser and reopen it
Mac OS
1. Go to System Preferences → Accessibility → Subtitles & Captioning → Create New Style
2. Set the color you like according to your preferences (if you want the background of the subtitle to be transparent, you can set the opacity in the background to transparent)
3. Close the Safari browser and reopen it
iOS & tvOS
1. Go to Settings → Accessibility → Subtitles & Captioning → Style → Create New Style
2. On the BACKGROUND change the Opacity to 0%
3. Close the browser or CATCHPLAY+ App and reopen it
Android
Android system currently does not support changing the subtitle background color.
Subtitle Size
Windows 10 & above
1. Click Start on your laptop/computer
2. Go to Settings → Ease of Access → Closed captioning
3. Click on Caption Size and adjust with your desired size
4. Close the Chrome browser and reopen it
Mac OS
1. Go to System Preferences → Accessibility → Subtitles & Captioning → Create New Style
2. Tap on Size and adjust with your desired size
3. Close the browser and reopen it
iOS & tvOS
1. Go to Settings → Accessibility → Subtitles & Captioning → Style → Create New Style
2. Tap on Size located under the Text section and adjust with your desired size
3. Close the browser or CATCHPLAY+ App and reopen it
Android
1. Open your device's Settings app
2. Tap Accessibility, then tap Caption preferences
3. Tap Caption size and style
4. To change caption size, tap Text size, then select the desired text size
5. Close Chrome browser or CATCHPLAY + App and reopen it