The commandbar is defined with a width of 100% and a padding of .5em. Browsers as Firefox and Chrome use a box-sizing model "content-box" as default. In this model padding and border are added to the defined width of the element, which results in a width of over 100% and (depending on the theme) will lead to ugly horizontal scrollbars.

I would suggest adding the following lines to the rule

.path-mod-scheduler div.commandbar {

    width: 100%;

    margin-left: auto;

    margin-right: auto;

    background-color: #eee;

    padding: 0.5em;

+    box-sizing: border-box;

+    -moz-box-sizing: border-box;

+    -webkit-box-sizing: border-box;

}

This forces a display with the box model "border-box". In this model the width includes padding and border.