Rambox-CE/ext/packages/ext-theme-base/sass/src/resizer/SplitterTracker.scss

.#{$prefix}resizable-overlay {
    position: absolute;
    left: 0;
    top: 0;
    
    width: 100%;
    height: 100%;
    
    display: none;
    
    z-index: 200000;
    
    background-color: #fff;
        
    @include opacity(0);
}