Change colour of the entire report if the base size goes below a certain value

Hi BalaR​,

Thank you for reaching out.

Here are a few posts that may help.

Change background and font color of widgets in Sisense

Highlight Bars with Above/Below Average Values in a Column Chart

Set The Background Color Of An Indicator

Highlight Max and Min values in Line chart

Using a combination of the conditional formatting and background customization, you should be able to change the Widget background dynamically. 

If that doesn't help, I have a few questions that will help us determine the best way forward for you.

1. What kind of report widget are you using?
2. Do you want the background of an individual Widget to change, or the background an entire Dashboard with multiple Widgets on it?