@media only screen {
  body {
    font-size: 85px;
  }
}
@media only screen and (max-width: 1200px) {
  body {
    font-size: 70px;
  }
}
@media only screen and (max-width: 900px) {
  body {
    font-size: 65px;
  }
}
html, body {
  background: #0f0f0f;
  height: 100%;
  font-family: "Work Sans";
}

.bg {
  background-attachment: fixed;
  background-color: #0f0f0f;
  background-position: 50% 50%;
  background-repeat: no-repeat;
  background-size: cover;
  height: 100%;
  filter: brightness(0.3);
  position: absolute;
  width: 100%;
}

.display {
  font-size: 100%;
  font-weight: 200;
  height: 15%;
  padding: 0 15px;
}

.history {
  font-size: 30%;
  font-weight: 400;
  height: 5%;
  padding: 0 15px;
}

.calculator {
  border: 3px solid #0f0f0f;
  border-radius: 25px;
  height: 85%;
  margin: 0 auto;
  min-height: 500px;
  min-width: 400px;
  opacity: 0.85;
  overflow: hidden;
  position: relative;
  top: 2.5%;
  transition: all 0.5s;
  width: 95%;
}
.calculator.on {
  box-shadow: 0 0 1rem #eeffee;
}
.calculator.on .btn-num {
  background-color: #eeffee;
}
.calculator.on .btn-oper {
  background-color: #58e83e;
}
.calculator.on .btn-func {
  background-color: #a2ff92;
}
.calculator.on .display {
  background-color: #0f4b0f;
  color: #eeffee;
}
.calculator.on .history {
  background-color: #0f4b0f;
  color: #2bd10e;
}
.calculator.off {
  box-shadow: 0 0 1rem #ffeeee;
}
.calculator.off .btn-num {
  background-color: #ffeeee;
}
.calculator.off .btn-oper {
  background-color: #e83e58;
}
.calculator.off .btn-func {
  background-color: #ff92a2;
}
.calculator.off .display {
  background-color: #4b0f0f;
  color: #ffeeee;
}
.calculator.off .history {
  background-color: #4b0f0f;
  color: #d10e2b;
}
.calculator .button-area {
  height: 80%;
  margin: 0;
  padding: 0;
  width: 100%;
}
.calculator .row {
  height: 20%;
  margin: 0;
  padding: 0;
}
.calculator .row:nth-child(4) {
  height: 40%;
}
.calculator .row:nth-child(4) .btn {
  height: 50%;
}
.calculator .row:nth-child(4) .btn#add {
  height: 100%;
}
.calculator .col-3 {
  line-height: 0;
  padding: 0;
}
.calculator .btn {
  border: 1px solid rgba(0, 0, 0, 0.2);
  border-radius: 0;
  box-sizing: border-box;
  color: #0f0f0f;
  font-family: "Work Sans";
  font-weight: 100;
  font-size: 60%;
  height: 100%;
  margin: 0;
  transition: all 0s;
  width: 100%;
}
.calculator .btn:hover {
  filter: brightness(0.9);
}
.calculator .btn:focus, .calculator .btn:hover {
  border: 1px solid rgba(0, 0, 0, 0.2);
  box-shadow: none;
  outline: none;
}

.creds {
  font-weight: 400;
  font-size: 25%;
  margin: 10px auto;
  position: relative;
  top: 2.5%;
}
.creds.on {
  color: #eeffee;
}
.creds.on a {
  color: #2bd10e;
}
.creds.off {
  color: #ffeeee;
}
.creds.off a {
  color: #d10e2b;
}