Time tracking app with React and Sass

Hi WandoCode, A wonderful solution you've got here. I love it!

With regards to your concern about the extra pixels of the parent element showing beneath the child's, you could remove the bottom border radii on the child element and set the parent to:

.parent {
    overflow: hidden;
}
/*where "X" and "Y" are set to sizes of your choice*/
.child {
    border-radius: Xpx Ypx 0 0; 
    width: 100%;
    display: block;
}

While you are at that, you could also fix your HTML validation issue, it's a great way to learn (it's already so commendable that you've got just a single issue ^_~).