main.css

body {
    background-color: #00807F;
    margin: 0px;
    -webkit-touch-callout: none; /* iOS Safari */
    -webkit-user-select: none; /* Safari */
    -khtml-user-select: none; /* Konqueror HTML */
    -moz-user-select: none; /* Old versions of Firefox */
    -ms-user-select: none; /* Internet Explorer/Edge */
    user-select: none; /* Non-prefixed version, currently
                                  supported by Chrome, Edge, Opera and Firefox */
}

/*https://github.com/AlexBSoft/win95.css/blob/master/assets/win95.css*/

progress {
    width: 100%;
    height: 1rem;
    overflow: hidden;
    font-size: .75rem;
    background-color: silver;
    border-radius: 0rem;
    border: 1px inset #d5d5d5;
    background-color: #1a0094;
    margin-block-start: 10px;
    margin-block-end: 10px;
    color: #1a0094;
}

    progress::-moz-progress-bar {
        background: #1a0094;
    }

    progress::-webkit-progress-value {
        background: #1a0094;
    }

.window {
    max-width: 500px;
    margin: auto;
}

#upgrades, #help {
    position: absolute;
    top: 10%;
    left: 0;
    right: 0;
    margin-left: auto;
    margin-right: auto;
    max-width: 90%;
}

@media only screen and (min-width: 500px) {
    body {
        margin: 5vh 0;
    }

    #upgrades, #help {
        max-width: 450px;
    }
}

@media only screen and (max-width: 499px) {
    #main {
        min-height: calc(100vh - 6px);
    }
}

.hidden {
    display: none;
}

.strikethrough {
    text-decoration: line-through;
}