Learn Accessibility by Building a Quiz - Step 46

Please I don’t really understand the color-contrast ratio, someone help me out please

body {
  background: #f5f6f7;
  color: #1b1b32;
  font-family: Helvetica;
  margin: 0;
}

header {
  width: 100%;
  height: 50px;
  background-color: #1b1b32;
  display: flex;
}

#logo {
  width: max(100px, 18vw);
  background-color: #0a0a23;
  aspect-ratio: 35 / 4;
  padding: 0.4rem;
}

h1 {
  color: #f1be32;
  font-size: min(5vw, 1.2em);
}

nav {
  width: 50%;
  max-width: 300px;
  height: 50px;
}

nav > ul {
  display: flex;
  justify-content: space-evenly;
}

nav > ul > li {
  color: #dfdfe2;
  margin: 0 0.2rem;
  padding: 0.2rem;
  display: block;
}

 li > a{
   color-contrast: 7:1;
 }

h1,
h2 {
  font-family: Verdana, Tahoma;
}

h2 {
  border-bottom: 4px solid #dfdfe2;
}

p::before {
  content: "Question #";
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

Please post a link to the challenge