odoo_source/addons/web/static/src/scss/web_calendar.scss

@keyframes backgroundfade {
    from {background-color: rgba($o-brand-odoo, 0.5);}
    to {background-color: #f5f5f5;}
}

.o_calendar_container {
    height: 100%;
    @include o-webclient-padding($top: $o-horizontal-padding/2, $bottom: $o-horizontal-padding/2);
    display: flex;

    @for $index from 1 through $o-nb-calendar-colors {
        .o_calendar_color_#{$index} {
            color: #0D0D0D;
            background-color: adjust-hue(rgb(255, 192, 192), (360/($o-nb-calendar-colors+1) * $index) * 1deg);
            border-color:  adjust-hue(rgb(255, 192, 192), (360/($o-nb-calendar-colors+1) * $index) * 1deg);
            opacity: 0.7;
            &.o_event_hightlight {
                font-weight: bold;
                opacity: 0.9;
            }
            &:hover {
                color: #666 !important;
            }
        }
        .o_underline_color_#{$index} {
            border-bottom: 4px solid adjust-hue(rgba(255, 192, 192, 0.7), (360/($o-nb-calendar-colors+1) * $index) * 1deg);
        }
    }

    .o_calendar_view {
        flex: 1 1 auto;
        min-width: 0;

        .o_calendar_widget {
            height: 100%;
            background-color: $o-view-background-color;
            * {
                z-index: 0; // FIXME
            }
            .fc-week-number, .fc-widget-header {
                background-color: lighten($o-brand-secondary, 30%);
            }
            .o_avatar_square {
                border-radius: 5px;
                display: inline-block;
                opacity: 1;
                border: 1px solid #999;
            }
            .o_fields img, .o_avatar_square {
                vertical-align: middle;
                margin-left: 1px;
                width: 18px;
                height: 18px;
            }
            .o_field_type_char:first-child {
                font-weight: bold;
            }
            .fc-view {
                overflow-x: auto;
            }
        }
    }

    .o_calendar_sidebar_container {
        flex: 0 0 $o-horizontal-padding;
        position: relative;

        &.o_sidebar_hidden {
            margin-right: -$o-horizontal-padding; // hack to display the toggler in the gutter
            .o_calendar_sidebar_toggler {
                padding: 4px;
                color: darken($o-webclient-background-color, 30%);
            }
        }

        .o_calendar_sidebar_toggler {
            @include o-position-absolute($top: 0, $right: 0);
            cursor: pointer;
            padding: 6px;
            z-index: 1;
            &:hover {
                color: black;
            }
        }

        .o_calendar_sidebar {
            width: 250px;
            margin-left: 8px;
            background: $o-view-background-color;
        }

        .ui-datepicker {
            width: 100%;
            font-size: 8pt;
            border-radius: 0;
            border: none;
            padding: 0;

            .ui-widget-header {
                display: flex;
                background: none;
                background-color: lighten($o-brand-secondary, 30%);
                border-radius: 0;

                .ui-datepicker-prev, .ui-datepicker-next {
                    flex: 0 0 auto;
                    position: static;
                    cursor: pointer;
                    padding: 2px;
                    text-align: center;
                    color: $o-main-text-color;
                    &.ui-state-hover {
                        background: none;
                        border: none;
                        color: black;
                    }
                    .ui-icon {
                        display: none;
                    }
                }
                .ui-datepicker-prev {
                    order: 1;
                    &:after {
                        font-family: FontAwesome;
                        content: "";
                    }
                }
                .ui-datepicker-next {
                    order: 3;
                    &:before {
                        font-family: FontAwesome;
                        content: "";
                    }
                }
                .ui-datepicker-title {
                    flex: 0 0 auto;
                    order: 2;
                    display: inline-block;
                    margin: 0 10px;
                }
            }
            table {
                td {
                    padding: 0 2px 2px 0;
                    background-color: $o-view-background-color;
                    a {
                        border: none;
                        background: none;
                        background-color: lighten($o-brand-secondary, 40%);
                        text-align: center;
                    }
                }
                .ui-state-default {
                    color: $o-brand-odoo;
                    &:hover {
                        background: none;
                        background-color: rgba($o-brand-odoo, 0.5);
                        border-color: $o-brand-odoo;
                        color: $o-view-background-color;
                    };
                }
                .ui-state-active {
                    background: none;
                    background-color: $o-brand-odoo;
                    color: $o-view-background-color;
                }
                .o_selected_range.o_color {
                    background: none;
                    background-color: $o-brand-odoo;
                    animation: backgroundfade 3s forwards;
                }
            }
        }
        .o_calendar_filter {
            padding: 8px;
            border-top: 1px solid lightgray;
            .o_field_many2one {
                width: 100%;
            }
        }
    }

    .fc-time-grid-event.fc-short .fc-time:before {
        content: '';
    }
}

.modal {
    .o_attendee_head {
        width: 32px;
        margin-right: 5px;
    }
}

.o_dashboard {
    .o_calendar_container .o_calendar_sidebar_container {
        display: none;
    }
}

// Mobile rules
@include media-breakpoint-down(sm) {
    .o_calendar_container {
        padding: 0;
    }
}
@include media-breakpoint-down(sm) {
    .o_control_panel {
        .o_calendar_button_today {
            float: right;
            > .o_calendar_text {
                margin-top: 3px;
            }
        }
    }
    .o_calendar_view {
        .fc-day-header {
            word-spacing: 1000px; // force line break in week mode
        }
    }
}