* {
    box-sizing: border-box;
    padding: 0;
    margin: 0;
}

body {
    height: 100vh;
    background-color: black;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

main {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background-color: black;
    padding: 10px 20px 10px;
    min-width: 300px;
    max-width: 400px;
    width: 75%;
    /* height: 90vh; */
}

main .input_container {
    width: 90%;
    display: flex;
    justify-content: center;
    align-items: center;
    flex: 1.5;
}
main .input_container input {
    flex: 1;
    height: 50px;
    text-align: right;
    background: none;
    color: #fff;
    font-size: 30px;
    width: 100%;
    border: none;
    outline: none;
}
main .operator_container {
    width: 100%;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    /* background-color: yellow; */
    flex: 4;
    gap: 10px;
}

main .operator_container .segment {
    width: 100%;
    display: flex;
    justify-content: center;
    flex: 1;
    gap: 10px;
}

button {
    flex: 1;
    border-radius: 50%;
    border: none;
    height: 60px;
    width: 60px;
}
#zero {
    flex: 2;
    border-radius: 40px;
    text-align: left;
    padding: 0 0 0 20px;
}

/* button colors */
.deep_grey {
    background-color: #626161;
    color: #fff;
    font-size: 20px;
    font-weight: bold;
}
.light_grey {
    background-color: #b1b1b1;
    font-size: 20px;
    font-weight: bold;
}
.orange {
    background-color: orange;
    color: #fff;
    font-size: 20px;
    font-weight: bold;
}

.active_operator {
    background-color: white;
    color: orange;
}

@keyframes flash {
    0% { background-color: orange; color: white; }
    50% { background-color: white; color: orange; }
    100% { background-color: orange; color: white; }
}

.flash-effect {
    animation: flash 0.3s ease-in-out;
}

@media(min-width: 580px) {
    button {
        height: 4em;
        /* width: 100%; */
    }
    #zero {
        border-radius: 50px;
    }
}