I know you can use a browser extension like Stylus to override some of roll20's styles. Here's an example of what I do with macrobar /*macro quickbar */
#macrobar {
height: auto !important;
width: 92% !important;
background-color: rgba(0, 0, 0, 0.44) !important;
text-align: center !important;
margin-left: 60px !important;
}
div.macrobox button.btn {
padding: 0 4px 0 4px;
font-size: 1.5rem;
line-height: 1.8rem;
margin: 0px 0 2px 0;
}
#macrobar_macros {
white-space: normal !important;
margin-left: 1% !important;
margin-right: 1% !important;
padding-bottom: 0px !important;
}
#macrobar .macrobox {
margin: 1px 5px 1px 5px ;
}
#macrobar div.macrobox:hover,
#macrobar div.macrobox.ui-sortable-helper {
padding-right: 12px;
margin-right: -7px;
border-radius: 3px;
background-color: #999;
cursor: move;
}