:root {
    /* Global variables */
    --doddle-gray: #444444;
    --doddle-font: "Roboto", sans-serif;
    --doddle-orange: #ff6600;
    --doddle-white: #ffffff;
}

/* * {
    box-sizing: border-box;
  } */

body {
    color: var(--doddle-gray);
    font-family: var(--doddle-font);
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
}

.main {
    background-color: var(--doddle-gray);
    border-style: none;
    position: relative;
    margin: 0;
    padding: 0 0 20px 0;
    min-height: 100vh;
}

.content {
    text-align: center;
    position: relative;
    padding: 10px;
}

.interface button i {
    font-size: 2.5rem;
    font-weight: bold;
}

.interface button {
    background-color: var(--doddle-orange);
    border-radius: 10px;
    border-style: none;
    color: var(--doddle-white);
    font-size: 1.5rem;
    font-weight: bold;
    width: 80px;
    height: 50px;
    margin-left: 10px;
    margin-top: 10px;
    transition: 0.1s;
    box-shadow: 3px 3px 3px 3px black;
}

.interface button:hover {
    background-color: var(--doddle-gray);
    cursor: pointer;
    box-shadow: 0px 0px 0px 0px;
    border: 1px solid black;
}

.interface {
    display: flex;
    justify-content: flex-end;
}

/* Help text */
.tooltip {
    position: relative;
}

.tooltip .tooltiptext {
    visibility: hidden;
    width: 40vw;
    background-color: var(--doddle-white);
    border: 2px solid var(--doddle-gray);
    color: var(--doddle-orange);
    text-align: left;
    border-radius: 6px;
    padding: 5px;
    position: absolute;
    z-index: 1;
    bottom: 150%;
    right: 15%;
    margin-right: -55px;
    opacity: 0;
    transition: opacity 0.3s;
    box-shadow: 5px 5px 5px 5px black;
    font-size: 1.3rem;
    font-weight: 500;
    font-family: var(--doddle-font);
}

.tooltip .tooltiptext::after {
    content: "";
    position: absolute;
    top: 100%;
    right: 15%;
    margin-right: -3px;
    border-width: 15px;
    border-style: solid;
    border-color: var(--doddle-white) transparent transparent transparent;
}

.tooltip:hover .tooltiptext {
    visibility: visible;
    opacity: 1;
}

.screen {
    background-color: var(--doddle-white);
    border-radius: 10px;
    padding: 50px 50px 25px 50px;
    margin: 5px auto;
}

.startPanel {
    background-color: var(--doddle-white);
    border-radius: 5px;
    border-color: navy;
    border-width: 3px;
    border-style: solid;
    font-size: 2rem;
    color: navy;
    top: 40%;
    left: 50%;
    transform: translate(-50%, -50%);
    padding: 25px;
    min-width: 40%;
    box-shadow: 10px 10px 10px 0px black;
}

.startPanel button {
    border: 2px solid var(--doddle-orange);
    padding: 10px 20px;
    font-size: 2rem;
    color: var(--doddle-orange);
    border-radius: 10px;
}

.startPanel button:hover {
    background-color: var(--doddle-orange);
    color: var(--doddle-white);
    cursor: pointer;
}

.intro img {
    width: 600px;
}

.heading {
    color: var(--doddle-gray);
    text-align: center;
    font-size: 1.8rem;
    text-transform: capitalize;
}

.intro,
.startPanel {
    position: absolute;
}

/* Content_________________________________________________________________ */
.classroom {
    padding: 20px;
    border: 3px solid navy;
    background: url(images/wooden-table.jpg);
    background-position: center;
    background-repeat: no-repeat;
    background-size: cover;
}

.calculator {
    width: 30%;
    margin: auto;
    background-color: var(--doddle-gray);
    border-radius: 50px 50px 25px 25px;
    padding: 20px;
    border: 5px solid black;
}

.display {
    background-color: rgb(0, 255, 128);
    margin: 20px auto 0 auto;
    padding: 20px;
    border-radius: 5px;
    border: 2px solid black;
    font-size: 2rem;
    color: black;
    text-align: right;
}

.row {
    display: flex;
    justify-content: space-between;
    margin: 10px auto;
}

.invisible {
    visibility: hidden;
}

.row span {
    background-color: #999999;
    border: 2px solid #111111;
    padding: 5px 10px;
    margin: 0;
    width: 20%;
    color: black;
    font-size: 3rem;
    font-weight: bold;
    border-radius: 5px;
    user-select: none;
}

.row span:hover {
    cursor: pointer;
    background-color: var(--doddle-orange);
}

@media screen and (max-width: 749px) {
    .calculator {
        width: 90%;
    }
}