@salesforce-ux/design-system/css/data-tables/fixed-header/index.css

Salesforce Lightning Design System

/*! Lightning Design System 2.12.0 */
@charset "UTF-8";
.slds-table_header-fixed_container {
  position: relative;
  padding-top: 2rem;
  background-color: #fafaf9;
  overflow: hidden;
}
.slds-table_header-fixed_container:before {
  border-bottom: 1px solid #dddbda;
  content: "";
  display: block;
  position: relative;
  width: 100%;
}

.slds-cell-fixed {
  background-color: #fafaf9;
  position: absolute;
  top: 0;
  min-height: 2rem;
}

.slds-table_header-fixed {
  border-top: 0;
}
.slds-table_header-fixed thead th {
  position: static;
  padding: 0;
  border-top: 0;
}
.slds-table_header-fixed tbody tr:first-child td,
.slds-table_header-fixed tbody tr:first-child th {
  border-top: 0;
}