body {
  background-image: url(../images/brick-wall.jpg);
}

button {
  height: 100px;
  width: 100px;
  align-items: center;
  font-size: 40px;
}

.flex-container {
    display:flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: center;
    align-content: flex-start;
    align-items: stretch;
    /*border: 2px solid black;*/
    font-size: 40px;
}


.flex-items-default {
    width: 300px;
    height: 250px;
    flex-grow: 0;
    flex-shrink: 0;
    flex-basis: 0;
}

 .flex-calc-button {
    width: 100px;
    height: 100px;
    border: 2px solid black;
    border-radius: 5px;
    background-color: silver;
}


.flex-item-screen {
   width: 408px;
   height: 150px;
   border: 4px solid black;
   border-radius: 5px;
   background-color: lightslategrey;

}

button:hover {
  border: 1px solid red;
}