The highlighted parts are what I added to Scott's slim theme.
/* override tethys core styles */
#app-header .tethys-app-header {
height: 60px;
}
#app-header .tethys-app-header .toggle-nav {
margin-top: 10px;
}
#app-header .tethys-app-header .icon-wrapper img {
height: 50px;
}
#app-header .tethys-app-header .icon-wrapper {
margin-left: 15px;
padding: 5px 10px;
}
#app-header .tethys-app-header .app-title-wrapper .app-title {
padding: 0;
padding-left: 65px;
}
#app-header .tethys-app-header .exit-button {
margin-top: 10px;
}
#app-header .tethys-app-header .exit-button a {
padding: 5px 10px;
}
#app-content-wrapper #app-content {
height: 100vh;
padding-top: 60px;
padding-bottom: 50px;
}
#app-content-wrapper #app-content #app-actions {
height: 50px;
padding-top: 5px;
}
#app-content-wrapper #app-content #app-navigation {
padding-top: 60px;
}
#app-content-wrapper #app-content #inner-app-content {
overflow-y: auto;
}