zulip/static/styles/alerts.css

$alert-red: hsl(16, 60%, 45%);
$alert-error-red: hsl(0, 80%, 40%);

.alert-display {
    display: none;

    &.show {
        display: block;
    }
}

.alert-animations {
    &.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;
    }
}

/* alert box component changes */
.alert-box {
    position: absolute;
    top: 0;
    left: 0;
    width: 900px;
    margin-left: calc(50% - 450px);
    z-index: 220;
    max-height: 100%;
    overflow-y: auto;
    overscroll-behavior: contain;

    .stacktrace {
        @extend .alert-display, .alert-animations;

        font-size: 1rem;
        color: hsl(0, 80%, 40%);

        margin-top: 5px;
        padding: 1rem 0;

        background-color: hsl(0, 100%, 98%);
        border-radius: 4px;
        border: 1px solid hsl(0, 80%, 40%);
        box-shadow: 0 0 2px hsl(0, 80%, 40%);

        .stacktrace-header {
            display: flex;
            justify-content: space-between;

            .message {
                flex: 1 1 auto;
            }

            .warning-symbol,
            .exit {
                flex: 0 0 auto;
                font-size: 1.3rem;
                padding: 0 1rem;
            }

            .exit::after {
                cursor: pointer;
                font-size: 2.3rem;
                content: "\d7";
            }
        }

        .stacktrace-content {
            font-family: "Source Code Pro", monospace;
            font-size: 0.85rem;

            margin-top: 1rem;

            .stackframe {
                padding-left: calc(3.3rem - 14px);
                padding-right: 1rem;
            }
        }

        .expand {
            cursor: pointer;
            color: hsl(0, 32%, 83%);

            &:hover {
                color: hsl(0, 0%, 20%);
            }
        }

        .subtle {
            color: hsl(0, 7%, 45%);
        }

        .code-context {
            color: hsl(0, 7%, 15%);
            background-color: hsl(0, 7%, 98%);
            box-shadow: inset 0 11px 10px -10px hsl(0, 7%, 70%),
                inset 0 -11px 10px -10px hsl(0, 7%, 70%);

            margin-top: 1em;
            margin-bottom: 1em;

            .code-context-content {
                padding: 1rem 0;
                white-space: pre;
                overflow-x: auto;
            }

            .line-number {
                width: 3rem;
                display: inline-block;
                text-align: right;
                color: hsl(0, 7%, 35%);
            }

            .focus-line {
                background-color: hsl(0, 7%, 90%);
                width: 100%;
            }
        }
    }

    .alert {
        @extend .alert-animations;

        font-size: 1rem;
        border-radius: 4px;
        background-color: hsl(0, 0%, 100%);

        position: relative;

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

        text-shadow: none;

        color: $alert-red;
        border: 1px solid $alert-red;
        box-shadow: 0 0 2px $alert-red;

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

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

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

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

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

            &::before {
                color: $alert-error-red;
            }
        }

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

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

            cursor: pointer;

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

/* animation section */
@keyframes fadeIn {
    0% {
        display: block;
        opacity: 0;
        transform: translateY(-100px);
    }

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

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

    100% {
        display: none;
        opacity: 0;
        transform: translateY(-100px);
    }
}

/* @media queries */
@media (width < $lg_min) {
    .alert-box {
        width: 80%;
        left: 10%;
        margin-left: 0;
    }
}