style.css

:root {
    --digit-keys: #333333;
    --operator-keys: #F1A33B;
    --operator-sci-keys: #212121;
    --background-color: #000000;
    --function-keys: #A5A5A5;
    --header-height: 104px;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    user-select: none;
    font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
    height: 100%;
}

body {
    background-color: var(--background-color);
    color: #ffffff;
}

sup {
  font-size: 0.6em;
}

header {
  box-sizing: border-box;
  border-width: 2px;
  border-style: solid;
  border-color: var(--background-color);
  height: var(--header-height);
  background-color: var(--background-color);
}

/* vertical(mobile) first */
main {
  font-size: 4.5rem;
}

main.tables {
  display: flex;
  flex-direction: row;
  height: calc(100% - var(--header-height));
}

section {
  border-spacing: 0px;
  width: 100%;
  height: 100%;
}

section#sci {
  display: none;
}

.row {
  width: 100%;
  height: 20%;
  display: flex;
}

.sub-col {
  /* display: flex;
    justify-content: center;
    align-items: center;
    width: 21%;
    height: 86%;
    -webkit-box-flex: 0;
    -ms-flex: 0 0 21%;
    flex: 0 0 21%;
    max-width: 21%;
    border-radius: 50%;
    transition: background-color .8s ease-out; */

  display: inline-flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  margin: 0;
  padding: 0;
  width: 25%;
  height: 100%;
  border-radius: 50%;
  color: #ffffff;

  border-width: 1vh;
  border-style: solid;
  border-color: var(--background-color);
}

.input {
  display: flex;
  align-items: flex-end;
  justify-content: end;
  height: 100%;
  font-size: 6.1em;
  font-weight: bold;
  overflow-x: hidden;
}

.input {
  padding: 10px;
  /* background-color: violet; */
  text-align: right;
}

.sub-col p {
  margin: 0;
  padding: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

/* button */
div[button-type='digit'] {
  background-color: var(--digit-keys);
}

div[button-type='func'] {
  background-color: var(--function-keys);
  color: var(--background-color);
  /* animation: background-anim-fn .8s ease-out; */
}

div[button-type='operator'] {
  background-color: var(--operator-keys);
}

div[button-type='operator-sci'] {
  background-color: var(--operator-sci-keys);
}

#zero {
  width: 50% !important;
  border-radius: 500px;
}

#equal {
  /* animation: background-anim-equals .8s ease-out; */
}

/* .selected_operation[button-type='operator']:not(.selected_operation[id='equal']) {
    background-color: #d4d4d2;
    color: var(--operator-keys);
    transition: background-color, color .8s ease-out;
}

@keyframes background-anim-fn {
    0% { background-color: var(--function-keys); }
    50% { background-color: #fff;  }
    100% { background-color: var(--function-keys); }
}

@keyframes background-anim-equals {
    0% { background-color: var(--operator-keys); }
    50% { background-color: #fff;  }
    100% { background-color: var(--operator-keys); }
} */

@media screen and (min-aspect-ratio: 1/1) {
  body {
    --header-height: 150px;
  }

  main {
    font-size: 2.6rem;
  }

  section#sci {
    display: block;
    width: 60%;
  }

  section#normal {
    width: 40%;
  }
  
  section#sci .sub-col {
    width: 16.6667%;
  }
}