This is a theme for schedule-x which makes it look a bit more like shadcn, and removes a bit of mui design hints.

schedule-x-theme.css

:root {
  /* Primary colors */
  --sx-color-primary: hsl(var(--primary));
  --sx-color-on-primary: hsl(var(--primary-foreground));
  --sx-color-primary-container: hsl(var(--muted));
  --sx-color-on-primary-container: hsl(var(--muted-foreground));

  /* Secondary colors */
  --sx-color-secondary: hsl(var(--secondary));
  --sx-color-on-secondary: hsl(var(--secondary-foreground));
  --sx-color-secondary-container: hsl(var(--accent));
  --sx-color-on-secondary-container: hsl(var(--accent-foreground));

  /* Tertiary colors */
  --sx-color-tertiary: hsl(var(--muted));
  --sx-color-on-tertiary: hsl(var(--muted-foreground));
  --sx-color-tertiary-container: hsl(var(--accent));
  --sx-color-on-tertiary-container: hsl(var(--accent-foreground));

  /* Surface colors */
  --sx-color-surface: hsl(var(--background));
  --sx-color-surface-dim: hsl(var(--muted));
  --sx-color-surface-bright: hsl(var(--card));
  --sx-color-on-surface: hsl(var(--foreground));
  --sx-color-surface-container: hsl(var(--card));
  --sx-color-surface-container-low: hsl(var(--muted));
  --sx-color-surface-container-high: hsl(var(--accent));

  /* Background colors */
  --sx-color-background: hsl(var(--background));
  --sx-color-on-background: hsl(var(--foreground));

  /* Utility colors */
  --sx-color-outline: hsl(var(--border));
  --sx-color-outline-variant: hsl(var(--border));
  --sx-color-shadow: hsl(var(--border));
  --sx-color-surface-tint: hsl(var(--primary));

  /* Neutral colors */
  --sx-color-neutral: hsl(var(--foreground));
  --sx-color-neutral-variant: hsl(var(--muted-foreground));

  /* Internal colors */
  --sx-internal-color-gray-ripple-background: hsl(var(--muted));
  --sx-internal-color-light-gray: hsl(var(--muted));
  --sx-internal-color-text: hsl(var(--foreground));

  /* Radius */
  --sx-rounding-extra-small: 0.5rem;
  --sx-rounding-small: 0.75rem;
  --sx-rounding-extra-large: 1rem;

  /* Padding */
  --sx-spacing-padding1: 2px;
  --sx-spacing-padding2: 4px;
  --sx-spacing-padding3: 8px;
  --sx-spacing-padding4: 10px;
  --sx-spacing-padding6: 12px;
  --sx-spacing-modal-padding: 14px;
}

.sx-react-calendar-wrapper {
  width: 100%;
  max-width: 100%;
  /* spacing.20 is because the header is spacing.16 + spacing.4 for sidebar padding */
  height: calc(100svh - theme(spacing.20));
  margin: 0;
}

.sx__calendar {
  border: none;
}

.sx__view-selection-items {
  border-radius: var(--sx-rounding-small);
  overflow: hidden;
  margin-top: 10px;
  box-shadow: none;
  border-width: 1px;
  border-color: hsl(var(--border));
}

.sx__date-picker-popup {
  border-radius: var(--sx-rounding-small);
  overflow: hidden;
  margin-top: 10px;
  box-shadow: none;
  border-width: 1px;
  border-color: hsl(var(--border));
}


.sx__event-modal.sx__event-modal-default {
  overflow: hidden;
  box-shadow: none;
  border-width: 1px;
  border-color: hsl(var(--border));
}

.sx__forward-backward-navigation {
  display: flex;
  align-items: center;
  justify-self: center;
  gap: 6px;
}

.sx__chevron-wrapper {
  /* height: 100%;
  width: 100%; */
  min-width: 39px;
  min-height: 39px;
  border-radius: var(--sx-rounding-extra-small);
}

.sx__chevron.sx__chevron--next {
  border-width: 0.1rem 0.1rem 0 0;
}

.sx__chevron.sx__chevron--previous {
  border-width: 0.1rem 0.1rem 0 0;
}

.sx__date-input-chevron {
  content: url("data:image/svg+xml,%3c%3fxml version='1.0' encoding='utf-8'%3f%3e%3c!-- Uploaded to: SVG Repo%2c www.svgrepo.com%2c Generator: SVG Repo Mixer Tools --%3e%3csvg width='800px' height='800px' viewBox='0 0 24 24' fill='none' xmlns='http://www.w3.org/2000/svg'%3e%3cpath d='M6 9L12 15L18 9' stroke='black' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/%3e%3c/svg%3e");
}

.dark .sx__date-input-chevron {
  content: url("data:image/svg+xml,%3c%3fxml version='1.0' encoding='utf-8'%3f%3e%3c!-- Uploaded to: SVG Repo%2c www.svgrepo.com%2c Generator: SVG Repo Mixer Tools --%3e%3csvg width='800px' height='800px' viewBox='0 0 24 24' fill='none' xmlns='http://www.w3.org/2000/svg'%3e%3cpath d='M6 9L12 15L18 9' stroke='white' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/%3e%3c/svg%3e");
}


.sx__ripple::before,
.sx__ripple::after {
  all: unset !important;
}