#editor {
    position: absolute;
    font-size: 15px;
    top: 40px;
    right: 0;
    bottom: 0;
    left: 0;
}

#output-pane {
    padding: 8px;
    position: absolute;
    font-size: 15px;
    height: 143px;
    right: 0;
    bottom: 0;
    left: 0;
    border-top: 1px solid #ccc;
    background-color: #eee;
    overflow: auto;
    display: none;
    box-shadow: inset 0px 1px 10px rgba(0, 0, 0, 0.1);
}

#output-pane button.close {
    margin-right: 5px;
}

#output-pane .executing {
    display: none;
    font-weight: bold;
    color: #666;
}

#output pre.error {
    background-color: #eddddd;
    border-color: #ff0000;
    color: #600;
}

.popover input {
    margin-top: 10px;
}

.navbar li button {
    margin-left: 10px;
    margin-right: 10px;
}

.errorGutter {
    background-color: #ffcccc;
    color: #cc0000;
}

#editor {
    position: absolute;
    font-size: 15px;
    top: 40px;
    right: 0;
    bottom: 0;
    left: 0;
}

#output-pane {
    padding: 8px;
    position: absolute;
    font-size: 15px;
    height: 143px;
    right: 0;
    bottom: 0;
    left: 0;
    border-top: 1px solid #ccc;
    background-color: #eee;
    overflow: auto;
    display: none;
    box-shadow: inset 0px 1px 10px rgba(0, 0, 0, 0.1);
}

#output-pane button.close {
    margin-right: 5px;
}

#output-pane .executing {
    display: none;
    font-weight: bold;
    color: #666;
}

#output pre.error {
    color: #b94a48;
    background-color: #f2dede;
    border-color: #eed3d7;
}

.popover input {
    margin-top: 10px;
}

.navbar li button {
    margin-left: 10px;
    margin-right: 10px;
}

.errorGutter {
    background-color: #ffcccc;
    color: #cc0000;
}

Change style of error message
Change style of error message
