.container {
  display: grid;
  
  grid-template:
    "header header"
    "sidebar maincontent"
    "footer"
    / 2fr 1fr;
  grid-gap: 10px;
}

header { grid-area: header; }
aside { grid-area: sidebar; }
main { grid-area: maincontent; }
footer { grid-area: footer; }