upstream-zulip/web/styles/alerts.css

:root {
    --color-alert-red: hsl(16deg 60% 45%);
    --color-alert-error-red: hsl(0deg 80% 40%);
}

.alert-display {
    display: none;

    &.show {
        display: block;
    }
}

.alert-animations {
    /* TODO: Remove these animations in favour of those
       in web/styles/banners.css, once all the alert popups
       have been converted to use the new banner component. */
    &.show {
        animation-name: fadeIn;
        animation-duration: 0.3s;
        animation-fill-mode: forwards;
    }

    &.fade-out {
        animation-name: fadeOut;
        animation-duration: 0.3s;
        animation-fill-mode: forwards;
    }

    .faded {
        opacity: 0.7;
    }
}

.home-error-bar {
    display: none;
}

/* alert box component changes */

#alert-popup-container {
    /* Ensure alert box remains in viewport, regardless of scroll
       position in message list. */
    position: fixed;
    /* Offset to account for the top padding + 5px from the top. */
    top: calc(5px + (-1 * var(--popup-banner-translate-y-distance)));
    left: 50%;
    transform: translateX(-50%);
    width: 100%;
    max-width: 900px;
    z-index: 220;
    max-height: 100%;
    overflow-y: auto;
    overscroll-behavior: contain;
    /* Set top padding to account for the translate-y motion of the
       animation to prevent the vertical scroll bar from appearing. */
    padding-top: var(--popup-banner-translate-y-distance);

    @media (width < $lg_min) {
        max-width: 90%;
    }
}

.alert-box {
    display: flex;
    /* Using column-reverse flex direction enables a stack-like
       behavior where the most recent alert is always on top. */
    flex-direction: column-reverse;
    justify-content: center;
    gap: 5px;

    .alert {
        @extend .alert-animations;

        box-sizing: border-box;
        width: 100%;
        border-radius: 4px;
        background-color: hsl(0deg 0% 100%);

        position: relative;

        /* gives room for the error icon and the exit button. */
        padding: 10px 50px;

        text-shadow: none;

        color: var(--color-alert-red);
        border: 1px solid var(--color-alert-red);
        box-shadow: 0 0 2px var(--color-alert-red);

        &::before {
            float: left;
            margin-left: -38px;

            font-family: FontAwesome;
            font-size: 1.3em;
            line-height: 1;
            overflow: hidden;
            content: "\f071";

            color: hsl(16deg 60% 55%);
        }

        &::after {
            clear: both;
            content: "";
            display: table;
        }

        &.alert-error {
            color: var(--color-alert-error-red);
            border: 1px solid var(--color-alert-error-red);
            box-shadow: 0 0 2px var(--color-alert-error-red);

            &::before {
                color: var(--color-alert-error-red);
            }
        }

        .exit {
            float: right;
            margin: -10px -50px -10px 0;
            padding: 13px 10px;

            font-size: 2.5em;
            font-weight: 300;
            line-height: 1ex;
            overflow: hidden;

            cursor: pointer;

            &::after {
                content: "\d7";
            }
        }
    }
}

/* animation section */
@keyframes fadeIn {
    0% {
        opacity: 0;
        transform: translateY(
            calc(-1 * var(--popup-banner-translate-y-distance))
        );
    }

    100% {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeOut {
    0% {
        opacity: 1;
        transform: translateY(0);
    }

    100% {
        opacity: 0;
        transform: translateY(
            calc(-1 * var(--popup-banner-translate-y-distance))
        );
    }
}

.update-read-flags-for-narrow-banner .banner-close-button {
    /* Disable pointer events to prevent user interaction,
       since this button is repurposed as a loading indicator. */
    pointer-events: none;
}