Check out example codes for "make footer stick to bottom without overlap over other elements". It will help you in understanding the concepts better.

Code Example 1

body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

#footer {
  background-color: #efefef;
  flex: 0 0 50px;/*or just height:50px;*/
  margin-top: auto;
}

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