main.css

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

html,
body {
    font-family: monospace;
}


/* WEBSITE NAME - HEADER */
.website-name {
    padding: 30px;
    text-align: center;
    transition: .3s ease;
}

.website-name #icon {
    font-size: 50px;
}



/* NAVBAR */
.nav {
    background-color: rgba(0, 0, 0, .1);
    position: sticky; top: 0;
    backdrop-filter: blur(4px);
    text-align: center;
    box-shadow: 0 0 8px rgba(0, 0, 0, 0.3);
}

.navBtn {
    margin: 10px 0;
}

.navBtn:hover {
    border: solid 2px rgb(80, 150, 250);
    box-shadow: 0 0 0 2px rgba(0, 0, 0, 0.1);
    background-color: rgba(190, 215, 255, .5);
    backdrop-filter: blur(4px);
}

.navBtn:active {
    border: solid 2px rgb(80, 120, 255);
    background-color: rgba(190, 215, 255, .7);
    backdrop-filter: blur(4px);
    box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.1);
}

.navUnselected {
    border: solid 2px rgb(230, 230, 230);
    background-color: rgba(240, 240, 240, .8);
    backdrop-filter: blur(4px);
    border-radius: 5px;
    padding :5px 30px;
    transition: .3s ease;
}

.navSelected {
    border: solid 2px rgb(80, 150, 250);
    border-radius: 5px;
    padding :5px 30px;
    transition: .2s ease;
    background-color: rgba(190, 215, 255, .6);
    backdrop-filter: blur(4px);
}



/* MAIN-CONTENT */
main {
    height: 100%;
    display: flex;
    justify-content: center;
    font-family: monospace;
    padding: 20px;
}

/* --- Calculators --- */
.calculators {
    display: grid;
    gap: 20px;
    grid-template-columns: repeat(2, 1fr);
    transition: .3 ease;
    margin: 30px 5px 80px 5px;
}

.calculator {
    text-align: center;
    border: solid 2px gainsboro;
    border-radius: 10px;
    max-width: 600px;
    padding: 30px 20px;
    transition: .3 ease;
}

.calculator h2 {
    font-size: 22px; 
    margin: 0 0 10px 0;
    transition: .3 ease;
}

.calculator p {
    margin: 5px;
    font-size: 15px;
}

.calculator span {
    display: inline-block;
    background-color: rgba(0, 0, 0, 0.1);
    border-radius: 5px;
    margin: 10px 0 0 0;
    padding: 3px 50px;
    border-bottom: solid 2px white;
    transition: .3s ease;
    font-family: monospace;
}

.calculator span:hover {
    box-shadow: 0 0 6px rgba(0, 0, 0, 0.2);
    border-bottom: solid 2px rgb(80, 150, 250);
    scale: 103%;
}

.calculator span:active {
    scale: 95%;
    box-shadow: 0 0 0 rgba(0, 0, 0, 0.2);
}

#cal_length {
    display: block;
}

#cal_weight {
    display: none;
}

#cal_volume {
    display: none;
}

/* --- Input --- */
.userInput {
    border: solid 2px white;
    border-radius: 5px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.3);
    padding: 2px;
    margin: 5px 5px;
    transition: 0.3s ease;
    font-family: monospace;
}

.userInput:hover {
    border: solid 2px rgb(80, 150, 250);
    border-radius: 5px;
    box-shadow: 0 0 0 5px rgb(80 150 250 / 30%);
}

.userInput:focus {
    outline: none;
    border: solid 2px rgb(80, 150, 250);
    border-radius: 4px;
    letter-spacing: 1px;
    box-shadow: 0 0 0 2px rgb(80 150 250 / 30%);
}

.userInput:active {
    background-color: rgb(190, 215, 255);
    border: solid 2px rgb(80, 150, 250);
    border-radius: 5px;
    box-shadow: 0 0 0 5px rgb(80 150 250 / 30%);
    scale: 102%;
}

/* --- Type Select --- */
.type {
    border: solid 2px rgb(0 0 0 / 50%);
    border-radius: 5px;
    box-shadow: 0 0 7px rgba(0, 0, 0, 0.2);
    padding: 1px;
    margin: 5px;
    transition: 0.3s ease;
    font-family: monospace;
}

.type:hover {
    border: solid 2px rgb(80, 150, 250);
    border-radius: 5px;
    box-shadow: 0 0 0 5px rgb(80 150 250 / 30%);
}

.type:focus {
    outline: none;
    border: solid 2px rgb(80, 150, 250);
    border-radius: 4px;
    box-shadow: 0 0 0 2px rgb(80 150 250 / 30%);
}

.type:active {
    background-color: rgb(190, 215, 255);
    border: solid 2px rgb(80, 150, 250);
    border-radius: 5px;
    box-shadow: 0 0 0 5px rgb(80 150 250 / 30%);
    scale: 102%;
}



/* FOOTER-CONTROLS */
.footer {
    display: inline-flex;
    position: fixed;
    bottom: 0;
    width: 100%;
    background-color: rgba(200, 200, 200, .6);
    backdrop-filter: blur(4px);
    transition: .3s ease;
    align-items: center;
    box-shadow: 0 0 8px rgba(0, 0, 0, 0.3);
}

.toggleContainer {
    background-color: rgba(255, 255, 255, .8);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    border: solid 1px gray;
    border-radius: 8px;
    box-shadow: 0 0 2px rgb(200, 200, 200);
    transition: .3s ease;
    width: 30px;
    height: 30px;
    padding: 10px;
    margin: 10px;
}

.toggleContainer:hover {
    box-shadow: 0 0 0 4px rgba(200, 200, 200, .3);
    scale: 115%;
}

.toggleContainer:active {
    box-shadow: 0 0 0 1px rgba(200, 200, 200, .3);
    scale: 95%;
}

#toggle {
    font-size: 20px;
    color: black;
    top: 40px;
    left: 40px;
    animation-name: toggle;
}

.dp {
    margin-left: auto;
    margin-right: 10px;
    outline: none;
    border: solid 2px rgb(0 0 0 / 50%);
    border-radius: 5px;
    padding: 1px;
    transition: 0.3s ease;
    font-family: monospace;
}


.dp:hover {
    border: solid 2px rgb(80, 150, 250);
    box-shadow: 0 0 0 2px rgba(0, 0, 0, 0.1);
}

.dp:active {
    border: solid 2px rgb(80, 120, 255);
    background-color: rgb(170, 200, 255);
    box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.1);
}

.dp option {
    background-color: white;
    margin: 20px;
}



@media only screen and (max-width: 500px) {
    /* WEBSITE NAME & ICON */
    .website-name {
        padding: 20px;
    }



    /* HEADER & NAVIGATION */
    .navBtn {
        padding: 5px 10px;
        margin: 8px 0;
    }

    /* MAIN CONTENT */
    /* --- Calculators --- */
    .calculators {
        grid-template-columns: 1fr;
    }

    .calculator h2 {
        font-size: 18px;
        font-weight: 100;
        margin: 0 0 10px 0;
    }


    /* FOOTER */
    .toggleContainer {
        margin: 6px;
    }
}