@mixin toolbox-button-base {
    background-color: $brand-gray;
    color: $black;
    padding: 0em;
    width: 40px;
    height: 40px;
    font-size: 1.500em;
}

@mixin toolbox-button-focus {
    outline: none;
}

@mixin toolbox-runButton-disabled {
    background-color: $brand-gray;
    color: $brand-dark-gray;
}

@mixin toolbox-runButton-hover {
    background-color: $toolbox-btn-active;
}

#toolbox {
    background-color: $brand-gray;
    border-bottom: 1px solid $brand-dark-gray;
    padding: 2px 3px;

    #runButton[disabled], #runButton[disabled]:hover {
        @include toolbox-runButton-disabled;
    }

    .toolbox-button {
        @include toolbox-button-base;
    }

    .toolbox-button:hover {
        @include toolbox-runButton-hover;
    }

    .toolbox-button:focus {
        @include toolbox-button-focus;
    }

    .box.is-dragover {
        background-color: grey;
    }

    .toolbox-separator {
        background-color: $brand-dark-gray;
        display: inline-block;
        height: 15px;
        margin: 0 5px;
        user-select: none;
        width: 2px;        
    }
}

@mixin toolbox-button-base {
    background-color: $brand-gray;
    color: $black;
    padding: 0em;
    width: 40px;
    height: 40px;
    font-size: 1.500em;
}

@mixin toolbox-button-focus {
    outline: none;
}

@mixin toolbox-runButton-disabled {
    background-color: $brand-gray;
    color: $brand-dark-gray;
}

@mixin toolbox-runButton-hover {
    background-color: $toolbox-btn-active;
}

#toolbox {
    background-color: $brand-gray;
    border-bottom: 1px solid $brand-dark-gray;
    padding: 2px 3px;
    z-index: 0;

    #runButton[disabled], #runButton[disabled]:hover {
        @include toolbox-runButton-disabled;
    }

    .toolbox-button {
        @include toolbox-button-base;
    }

    .toolbox-button:hover {
        @include toolbox-runButton-hover;
    }

    .toolbox-button:focus {
        @include toolbox-button-focus;
    }

    .box.is-dragover {
        background-color: grey;
    }

    .toolbox-separator {
        background-color: $brand-dark-gray;
        display: inline-block;
        height: 15px;
        margin: 0 5px;
        user-select: none;
        width: 2px;        
    }
}

Set z-index to 0 for proper rendering
Set z-index to 0 for proper rendering
