Add this code to the Custom CSS field on the Style tab of your widget’s settings:
.global-styles,
[class*="PairSliderPicture__Container-sc"] {
border: 10px solid #4d4d4f;
}
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Hi there, @CAT_Exteriors and welcome to the Community 
Thanks for sharing your code with us!
Your initial code added just a bottom border. I’ve slightly adjusted your code, and now it adds a border to the whole widget 
2 Likes