.x-page-container {
  box-sizing: border-box;
  position: relative;
  height: 100%;
  display: flex;
  flex-direction: column;
  background-color: #fff;
}

.x-page-container-header, .x-page-container-sub, .x-page-container-footer {
  flex: 0 0 auto;
}

.x-page-container-main {
  flex: 1 0 0;
  height: 0;
}