Why is CSS ineffective in the DreamWeaver editing environment?

Many of my friends encounter this situation when using DreamWeaver, as shown in the figure below.
Link the currently edited document to the CSS file and apply the defined CSS style to the page elements, but the effect is not displayed in DreamWeaver.
The main reason is that DreamWeaver has an additional style display toolbar, which allows you to easily design different media types, such as screens, handheld devices, and print output. Other supported media types include projection Devices, TTY (Television Type Devices), and TV media types. It also provides the ability to enable or disable the rendering of all styles by switching the CSS display button.
To open the toolbar, open the "View" menu of DreamWeaver and select "style rendering" under the "toolbar" sub-menu to open the toolbar panel in the DreamWeaver environment.
1. Screen
2. Print
3. Handheld devices
4. Projection device
5. TTY
6. TV
7. Open/close CSS
Click "open/close CSS" to activate the CSS style.