makeup.css

body {
  font-size: 20px;
  font-family: arial;
  color: black;
}

span {
  color: #0066ff;
}

input {
  font-size: 25px;
  width: 25%;
  padding: 5px 10px;
  margin: 8px 0;
  display: inline-block;
  border: 0.5px solid black;
  box-sizing: border-box;
  background-color: #f2f2f2;
}

p {
  font-size: 20px;
  text-align: center;
}

input[type=number], select {
  width: 100%;
  padding: 5px 10px;
  margin: 8px 0;
  display: inline-block;
  border: 0.5px solid black;
  box-sizing: border-box;
  background-color: #f2f2f2;
  text-align: center;
}

.logo {
  width: 30%;
  height: 10%;
}

div {
  padding: 5px 10px;
  margin: 8px 0;
  font-size: 18px;
}

a {
  color: #0066ff;
  font-weight: bold;
}

div.boxes {
  border: 0.5px solid black;
  background-color: #e5e5e5;
}

.result {
  color: #0066ff;
  font-weight: bold;
  font-size: 25px;
}

.result-negative {
  color: red;
  font-weight: bold;
  font-size: 25px;
}

p.hint {
  font-size: 15px;
}

.output {
  font-size: 15px;
}

.formula {
  font-size: 15px;
}

* {
  box-sizing: border-box;
}

.menu {
  float: left;
  width: 20%;
  text-align: center;
}

.menu a {
  padding: 8px;
  margin-top: 7px;
  display: block;
  width: 100%;
}

.main {
  float: left;
  width: 60%;
  padding: 0 20px;
}

.right {
  float: left;
  width: 20%;
  padding: 15px;
  margin-top: 7px;
  text-align: center;
}

.footer {
  background-color: #e5e5e5;
  text-align: center;
  padding: 10px;
  margin-top: 7px;
}

div.secondary_boxes {
  border: 0.5px solid black;
  background-color: #e5e5e5;
  height: 365px;
}

.calculator_box {
  float: left;
  width: 50%;
  margin-top: 0px;
}

.results_box {
  float: left;
  width: 50%;
  margin-top: 0px;
}

@media only screen and (max-width:620px) {

  /* For mobile phones: */
  .menu, .main, .right {
    width: 100%;
  }

  .calculator_box, .results_box {
    width: 100%;
  }

  input{
    width: 100%;
    padding: 5px 10px;
    margin: 8px 0;
    display: inline-block;
    box-sizing: border-box;
    background-color: #f2f2f2;
    text-align: center;
  }

  .logo {
    width: 10%;
    height: 2%;
  }

  .menu a {
    padding: 4px;
    margin-top: 3.5px;
    display: inline;
    width: 100%;
  }
}