You can change the border color around search with this CSS:
input[type="search"] {
border-color: #000;
}
Border around widget title”
h2.widget-title {
border: 2px solid #000;
}
Shadow around sidebar widget would be:
.sidebar .widget {
-webkit-box-shadow: 10px 10px 5px 0px rgba(0,0,0,0.75);
-moz-box-shadow: 10px 10px 5px 0px rgba(0,0,0,0.75);
box-shadow: 10px 10px 5px 0px rgba(0,0,0,0.75);
}
You can use this site to adjust the shadow CSS: https://www.cssmatic.com/box-shadow
Adding CSS: https://docs.generatepress.com/article/adding-css/