Step 1: Open the Theme Builder Custom CSS Utility
For SharePoint Online and SharePoint On-Premise 2019, please navigate to Site Contents > ShortPoint Deshboard > Theme Builder > (choose the type of TB you will be working with, Classic or Modern ) > Utilities > Custom CSS.
For SharePoint On-Premise 2013 and On-Premise 2016 , please navigate to Site Settings > Site collection Administration > ShortPoint Dashboard > Theme Builder > Customize my Site > Utilities > Custom CSS
Step 2: Copy your Custom CSS code
Please copy the code to modify the Tool-tip.
for changing the font size:
font-size = 100%;
Note: Choose the size based on how big you want your text to be
For Changing the text Color
color : red;
Note : Choose the color based on your preferred color
: choose the size (percentage) based on how big you want the tool tip to be and test after clicking the apply button before publishing to make sure its the correct size.you can also play around with changes you want to make on this stage
Step 3: Paste your Custom CSS code
Don't forget to Publish
your changes, so they will be applied on your SharePoint site.