Below theme.css code is for creating object border like sense focus, change hsl code based on the border color requirement.

theme.css

.qvt-sheet {
background: #000000 !important;
}
.qv-inner-object {
border: 1px solid hsl(49, 100%, 50%);
padding: 5px;
}

Conclusion:-

Custom theme helped me to get rid of the top padding from Text and Extension objects

Final theme folder will have three files after adding above one

1. abcd.qext

2. theme.json

3. theme.css